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  <div class="SECT1">
    <h1 class="SECT1"><a name="ACTIONS-FILE" id="ACTIONS-FILE">8. Actions
    Files</a></h1>

    <p>The actions files are used to define what <span class=
    "emphasis EMPHASIS c2">actions</span> <span class=
    "APPLICATION">Privoxy</span> takes for which URLs, and thus determines
    how ad images, cookies and various other aspects of HTTP content and
    transactions are handled, and on which sites (or even parts thereof).
    There are a number of such actions, with a wide range of functionality.
    Each action does something a little different. These actions give us a
    veritable arsenal of tools with which to exert our control, preferences
    and independence. Actions can be combined so that their effects are
    aggregated when applied against a given set of URLs.</p>

    <p>There are three action files included with <span class=
    "APPLICATION">Privoxy</span> with differing purposes:</p>

    <ul>
      <li>
        <p><tt class="FILENAME">match-all.action</tt> - is used to define
        which <span class="QUOTE">"actions"</span> relating to
        banner-blocking, images, pop-ups, content modification, cookie
        handling etc should be applied by default. It should be the first
        actions file loaded</p>
      </li>

      <li>
        <p><tt class="FILENAME">default.action</tt> - defines many exceptions
        (both positive and negative) from the default set of actions that's
        configured in <tt class="FILENAME">match-all.action</tt>. It is a set
        of rules that should work reasonably well as-is for most users. This
        file is only supposed to be edited by the developers. It should be
        the second actions file loaded.</p>
      </li>

      <li>
        <p><tt class="FILENAME">user.action</tt> - is intended to be for
        local site preferences and exceptions. As an example, if your ISP or
        your bank has specific requirements, and need special handling, this
        kind of thing should go here. This file will not be upgraded.</p>
      </li>

      <li>
        <p><span class="GUIBUTTON">Edit</span> <span class="GUIBUTTON">Set to
        Cautious</span> <span class="GUIBUTTON">Set to Medium</span>
        <span class="GUIBUTTON">Set to Advanced</span></p>

        <p>These have increasing levels of aggressiveness <span class=
        "emphasis EMPHASIS c2">and have no influence on your browsing unless
        you select them explicitly in the editor</span>. A default
        installation should be pre-set to <tt class="LITERAL">Cautious</tt>.
        New users should try this for a while before adjusting the settings
        to more aggressive levels. The more aggressive the settings, then the
        more likelihood there is of problems such as sites not working as
        they should.</p>

        <p>The <span class="GUIBUTTON">Edit</span> button allows you to turn
        each action on/off individually for fine-tuning. The <span class=
        "GUIBUTTON">Cautious</span> button changes the actions list to
        low/safe settings which will activate ad blocking and a minimal set
        of <span class="APPLICATION">Privoxy</span>'s features, and
        subsequently there will be less of a chance for accidental problems.
        The <span class="GUIBUTTON">Medium</span> button sets the list to a
        medium level of other features and a low level set of privacy
        features. The <span class="GUIBUTTON">Advanced</span> button sets the
        list to a high level of ad blocking and medium level of privacy. See
        the chart below. The latter three buttons over-ride any changes via
        with the <span class="GUIBUTTON">Edit</span> button. More fine-tuning
        can be done in the lower sections of this internal page.</p>

        <p>While the actions file editor allows to enable these settings in
        all actions files, they are only supposed to be enabled in the first
        one to make sure you don't unintentionally overrule earlier
        rules.</p>

        <p>The default profiles, and their associated actions, as pre-defined
        in <tt class="FILENAME">default.action</tt> are:</p>

        <div class="TABLE">
          <a name="AEN2780" id="AEN2780"></a>

          <p class="c3">Table 1. Default Configurations</p>

          <table border="1" frame="border" rules="all" class="CALSTABLE">
            <col width="1*" title="C1">
            <col width="1*" title="C2">
            <col width="1*" title="C3">
            <col width="1*" title="C4">

            <thead>
              <tr>
                <th>Feature</th>

                <th>Cautious</th>

                <th>Medium</th>

                <th>Advanced</th>
              </tr>
            </thead>

            <tbody>
              <tr>
                <td>Ad-blocking Aggressiveness</td>

                <td>medium</td>

                <td>high</td>

                <td>high</td>
              </tr>

              <tr>
                <td>Ad-filtering by size</td>

                <td>no</td>

                <td>yes</td>

                <td>yes</td>
              </tr>

              <tr>
                <td>Ad-filtering by link</td>

                <td>no</td>

                <td>no</td>

                <td>yes</td>
              </tr>

              <tr>
                <td>Pop-up killing</td>

                <td>blocks only</td>

                <td>blocks only</td>

                <td>blocks only</td>
              </tr>

              <tr>
                <td>Privacy Features</td>

                <td>low</td>

                <td>medium</td>

                <td>medium/high</td>
              </tr>

              <tr>
                <td>Cookie handling</td>

                <td>none</td>

                <td>session-only</td>

                <td>kill</td>
              </tr>

              <tr>
                <td>Referer forging</td>

                <td>no</td>

                <td>yes</td>

                <td>yes</td>
              </tr>

              <tr>
                <td>GIF de-animation</td>

                <td>no</td>

                <td>yes</td>

                <td>yes</td>
              </tr>

              <tr>
                <td>Fast redirects</td>

                <td>no</td>

                <td>no</td>

                <td>yes</td>
              </tr>

              <tr>
                <td>HTML taming</td>

                <td>no</td>

                <td>no</td>

                <td>yes</td>
              </tr>

              <tr>
                <td>JavaScript taming</td>

                <td>no</td>

                <td>no</td>

                <td>yes</td>
              </tr>

              <tr>
                <td>Web-bug killing</td>

                <td>no</td>

                <td>yes</td>

                <td>yes</td>
              </tr>

              <tr>
                <td>Image tag reordering</td>

                <td>no</td>

                <td>yes</td>

                <td>yes</td>
              </tr>
            </tbody>
          </table>
        </div>
      </li>
    </ul>

    <p>The list of actions files to be used are defined in the main
    configuration file, and are processed in the order they are defined (e.g.
    <tt class="FILENAME">default.action</tt> is typically processed before
    <tt class="FILENAME">user.action</tt>). The content of these can all be
    viewed and edited from <a href="http://config.privoxy.org/show-status"
    target="_top">http://config.privoxy.org/show-status</a>. The over-riding
    principle when applying actions, is that the last action that matches a
    given URL wins. The broadest, most general rules go first (defined in
    <tt class="FILENAME">default.action</tt>), followed by any exceptions
    (typically also in <tt class="FILENAME">default.action</tt>), which are
    then followed lastly by any local preferences (typically in <span class=
    "emphasis EMPHASIS c2">user</span><tt class="FILENAME">.action</tt>).
    Generally, <tt class="FILENAME">user.action</tt> has the last word.</p>

    <p>An actions file typically has multiple sections. If you want to use
    <span class="QUOTE">"aliases"</span> in an actions file, you have to
    place the (optional) <a href="actions-file.html#ALIASES">alias
    section</a> at the top of that file. Then comes the default set of rules
    which will apply universally to all sites and pages (be <span class=
    "emphasis EMPHASIS c2">very careful</span> with using such a universal
    set in <tt class="FILENAME">user.action</tt> or any other actions file
    after <tt class="FILENAME">default.action</tt>, because it will override
    the result from consulting any previous file). And then below that,
    exceptions to the defined universal policies. You can regard <tt class=
    "FILENAME">user.action</tt> as an appendix to <tt class=
    "FILENAME">default.action</tt>, with the advantage that it is a separate
    file, which makes preserving your personal settings across <span class=
    "APPLICATION">Privoxy</span> upgrades easier.</p>

    <p>Actions can be used to block anything you want, including ads,
    banners, or just some obnoxious URL whose content you would rather not
    see. Cookies can be accepted or rejected, or accepted only during the
    current browser session (i.e. not written to disk), content can be
    modified, some JavaScripts tamed, user-tracking fooled, and much more.
    See below for a <a href="actions-file.html#ACTIONS">complete list of
    actions</a>.</p>

    <div class="SECT2">
      <h2 class="SECT2"><a name="AEN2879" id="AEN2879">8.1. Finding the Right
      Mix</a></h2>

      <p>Note that some <a href="actions-file.html#ACTIONS">actions</a>, like
      cookie suppression or script disabling, may render some sites unusable
      that rely on these techniques to work properly. Finding the right mix
      of actions is not always easy and certainly a matter of personal taste.
      And, things can always change, requiring refinements in the
      configuration. In general, it can be said that the more <span class=
      "QUOTE">"aggressive"</span> your default settings (in the top section
      of the actions file) are, the more exceptions for <span class=
      "QUOTE">"trusted"</span> sites you will have to make later. If, for
      example, you want to crunch all cookies per default, you'll have to
      make exceptions from that rule for sites that you regularly use and
      that require cookies for actually useful purposes, like maybe your
      bank, favorite shop, or newspaper.</p>

      <p>We have tried to provide you with reasonable rules to start from in
      the distribution actions files. But there is no general rule of thumb
      on these things. There just are too many variables, and sites are
      constantly changing. Sooner or later you will want to change the rules
      (and read this chapter again :).</p>
    </div>

    <div class="SECT2">
      <h2 class="SECT2"><a name="AEN2886" id="AEN2886">8.2. How to
      Edit</a></h2>

      <p>The easiest way to edit the actions files is with a browser by using
      our browser-based editor, which can be reached from <a href=
      "http://config.privoxy.org/show-status" target=
      "_top">http://config.privoxy.org/show-status</a>. Note: the config file
      option <a href=
      "config.html#ENABLE-EDIT-ACTIONS">enable-edit-actions</a> must be
      enabled for this to work. The editor allows both fine-grained control
      over every single feature on a per-URL basis, and easy choosing from
      wholesale sets of defaults like <span class="QUOTE">"Cautious"</span>,
      <span class="QUOTE">"Medium"</span> or <span class=
      "QUOTE">"Advanced"</span>. Warning: the <span class=
      "QUOTE">"Advanced"</span> setting is more aggressive, and will be more
      likely to cause problems for some sites. Experienced users only!</p>

      <p>If you prefer plain text editing to GUIs, you can of course also
      directly edit the the actions files with your favorite text editor.
      Look at <tt class="FILENAME">default.action</tt> which is richly
      commented with many good examples.</p>
    </div>

    <div class="SECT2">
      <h2 class="SECT2"><a name="ACTIONS-APPLY" id="ACTIONS-APPLY">8.3. How
      Actions are Applied to Requests</a></h2>

      <p>Actions files are divided into sections. There are special sections,
      like the <span class="QUOTE">"<a href=
      "actions-file.html#ALIASES">alias</a>"</span> sections which will be
      discussed later. For now let's concentrate on regular sections: They
      have a heading line (often split up to multiple lines for readability)
      which consist of a list of actions, separated by whitespace and
      enclosed in curly braces. Below that, there is a list of URL and tag
      patterns, each on a separate line.</p>

      <p>To determine which actions apply to a request, the URL of the
      request is compared to all URL patterns in each <span class=
      "QUOTE">"action file"</span>. Every time it matches, the list of
      applicable actions for the request is incrementally updated, using the
      heading of the section in which the pattern is located. The same is
      done again for tags and tag patterns later on.</p>

      <p>If multiple applying sections set the same action differently, the
      last match wins. If not, the effects are aggregated. E.g. a URL might
      match a regular section with a heading line of <tt class="LITERAL">{
      +<a href="actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a>
      }</tt>, then later another one with just <tt class="LITERAL">{
      +<a href="actions-file.html#BLOCK">block</a> }</tt>, resulting in
      <span class="emphasis EMPHASIS c2">both</span> actions to apply. And
      there may well be cases where you will want to combine actions
      together. Such a section then might look like:</p>

      <table class="c4" border="0" width="100%">
        <tr>
          <td>
            <pre class="SCREEN">
  { +<tt class="LITERAL">handle-as-image</tt>  +<tt class=
"LITERAL">block{Banner ads.}</tt> }
  # Block these as if they were images. Send no block page.
   banners.example.com
   media.example.com/.*banners
   .example.com/images/ads/
</pre>
          </td>
        </tr>
      </table>

      <p>You can trace this process for URL patterns and any given URL by
      visiting <a href="http://config.privoxy.org/show-url-info" target=
      "_top">http://config.privoxy.org/show-url-info</a>.</p>

      <p>Examples and more detail on this is provided in the Appendix,
      <a href="appendix.html#ACTIONSANAT">Troubleshooting: Anatomy of an
      Action</a> section.</p>
    </div>

    <div class="SECT2">
      <h2 class="SECT2"><a name="AF-PATTERNS" id="AF-PATTERNS">8.4.
      Patterns</a></h2>

      <p>As mentioned, <span class="APPLICATION">Privoxy</span> uses
      <span class="QUOTE">"patterns"</span> to determine what <span class=
      "emphasis EMPHASIS c2">actions</span> might apply to which sites and
      pages your browser attempts to access. These <span class=
      "QUOTE">"patterns"</span> use wild card type <span class=
      "emphasis EMPHASIS c2">pattern</span> matching to achieve a high degree
      of flexibility. This allows one expression to be expanded and
      potentially match against many similar patterns.</p>

      <p>Generally, an URL pattern has the form <tt class=
      "LITERAL">&lt;domain&gt;&lt;port&gt;/&lt;path&gt;</tt>, where the
      <tt class="LITERAL">&lt;domain&gt;</tt>, the <tt class=
      "LITERAL">&lt;port&gt;</tt> and the <tt class=
      "LITERAL">&lt;path&gt;</tt> are optional. (This is why the special
      <tt class="LITERAL">/</tt> pattern matches all URLs). Note that the
      protocol portion of the URL pattern (e.g. <tt class=
      "LITERAL">http://</tt>) should <span class=
      "emphasis EMPHASIS c2">not</span> be included in the pattern. This is
      assumed already!</p>

      <p>The pattern matching syntax is different for the domain and path
      parts of the URL. The domain part uses a simple globbing type matching
      technique, while the path part uses more flexible <a href=
      "http://en.wikipedia.org/wiki/Regular_expressions" target=
      "_top"><span class="QUOTE">"Regular Expressions"</span></a> (POSIX
      1003.2).</p>

      <p>The port part of a pattern is a decimal port number preceded by a
      colon (<tt class="LITERAL">:</tt>). If the domain part contains a
      numerical IPv6 address, it has to be put into angle brackets
      (<tt class="LITERAL">&lt;</tt>, <tt class="LITERAL">&gt;</tt>).</p>

      <div class="VARIABLELIST">
        <dl>
          <dt><tt class="LITERAL">www.example.com/</tt></dt>

          <dd>
            <p>is a domain-only pattern and will match any request to
            <tt class="LITERAL">www.example.com</tt>, regardless of which
            document on that server is requested. So ALL pages in this domain
            would be covered by the scope of this action. Note that a simple
            <tt class="LITERAL">example.com</tt> is different and would NOT
            match.</p>
          </dd>

          <dt><tt class="LITERAL">www.example.com</tt></dt>

          <dd>
            <p>means exactly the same. For domain-only patterns, the trailing
            <tt class="LITERAL">/</tt> may be omitted.</p>
          </dd>

          <dt><tt class="LITERAL">www.example.com/index.html</tt></dt>

          <dd>
            <p>matches all the documents on <tt class=
            "LITERAL">www.example.com</tt> whose name starts with <tt class=
            "LITERAL">/index.html</tt>.</p>
          </dd>

          <dt><tt class="LITERAL">www.example.com/index.html$</tt></dt>

          <dd>
            <p>matches only the single document <tt class=
            "LITERAL">/index.html</tt> on <tt class=
            "LITERAL">www.example.com</tt>.</p>
          </dd>

          <dt><tt class="LITERAL">/index.html$</tt></dt>

          <dd>
            <p>matches the document <tt class="LITERAL">/index.html</tt>,
            regardless of the domain, i.e. on <span class=
            "emphasis EMPHASIS c2">any</span> web server anywhere.</p>
          </dd>

          <dt><tt class="LITERAL">/</tt></dt>

          <dd>
            <p>Matches any URL because there's no requirement for either the
            domain or the path to match anything.</p>
          </dd>

          <dt><tt class="LITERAL">:8000/</tt></dt>

          <dd>
            <p>Matches any URL pointing to TCP port 8000.</p>
          </dd>

          <dt><tt class="LITERAL">&lt;2001:db8::1&gt;/</tt></dt>

          <dd>
            <p>Matches any URL with the host address <tt class=
            "LITERAL">2001:db8::1</tt>. (Note that the real URL uses plain
            brackets, not angle brackets.)</p>
          </dd>

          <dt><tt class="LITERAL">index.html</tt></dt>

          <dd>
            <p>matches nothing, since it would be interpreted as a domain
            name and there is no top-level domain called <tt class=
            "LITERAL">.html</tt>. So its a mistake.</p>
          </dd>
        </dl>
      </div>

      <div class="SECT3">
        <h3 class="SECT3"><a name="AEN2998" id="AEN2998">8.4.1. The Domain
        Pattern</a></h3>

        <p>The matching of the domain part offers some flexible options: if
        the domain starts or ends with a dot, it becomes unanchored at that
        end. For example:</p>

        <div class="VARIABLELIST">
          <dl>
            <dt><tt class="LITERAL">.example.com</tt></dt>

            <dd>
              <p>matches any domain with first-level domain <tt class=
              "LITERAL">com</tt> and second-level domain <tt class=
              "LITERAL">example</tt>. For example <tt class=
              "LITERAL">www.example.com</tt>, <tt class=
              "LITERAL">example.com</tt> and <tt class=
              "LITERAL">foo.bar.baz.example.com</tt>. Note that it wouldn't
              match if the second-level domain was <tt class=
              "LITERAL">another-example</tt>.</p>
            </dd>

            <dt><tt class="LITERAL">www.</tt></dt>

            <dd>
              <p>matches any domain that <span class=
              "emphasis EMPHASIS c2">STARTS</span> with <tt class=
              "LITERAL">www.</tt> (It also matches the domain <tt class=
              "LITERAL">www</tt> but most of the time that doesn't
              matter.)</p>
            </dd>

            <dt><tt class="LITERAL">.example.</tt></dt>

            <dd>
              <p>matches any domain that <span class=
              "emphasis EMPHASIS c2">CONTAINS</span> <tt class=
              "LITERAL">.example.</tt>. And, by the way, also included would
              be any files or documents that exist within that domain since
              no path limitations are specified. (Correctly speaking: It
              matches any FQDN that contains <tt class="LITERAL">example</tt>
              as a domain.) This might be <tt class=
              "LITERAL">www.example.com</tt>, <tt class=
              "LITERAL">news.example.de</tt>, or <tt class=
              "LITERAL">www.example.net/cgi/testing.pl</tt> for instance. All
              these cases are matched.</p>
            </dd>
          </dl>
        </div>

        <p>Additionally, there are wild-cards that you can use in the domain
        names themselves. These work similarly to shell globbing type
        wild-cards: <span class="QUOTE">"*"</span> represents zero or more
        arbitrary characters (this is equivalent to the <a href=
        "http://en.wikipedia.org/wiki/Regular_expressions" target=
        "_top"><span class="QUOTE">"Regular Expression"</span></a> based
        syntax of <span class="QUOTE">".*"</span>), <span class=
        "QUOTE">"?"</span> represents any single character (this is
        equivalent to the regular expression syntax of a simple <span class=
        "QUOTE">"."</span>), and you can define <span class=
        "QUOTE">"character classes"</span> in square brackets which is
        similar to the same regular expression technique. All of this can be
        freely mixed:</p>

        <div class="VARIABLELIST">
          <dl>
            <dt><tt class="LITERAL">ad*.example.com</tt></dt>

            <dd>
              <p>matches <span class="QUOTE">"adserver.example.com"</span>,
              <span class="QUOTE">"ads.example.com"</span>, etc but not
              <span class="QUOTE">"sfads.example.com"</span></p>
            </dd>

            <dt><tt class="LITERAL">*ad*.example.com</tt></dt>

            <dd>
              <p>matches all of the above, and then some.</p>
            </dd>

            <dt><tt class="LITERAL">.?pix.com</tt></dt>

            <dd>
              <p>matches <tt class="LITERAL">www.ipix.com</tt>, <tt class=
              "LITERAL">pictures.epix.com</tt>, <tt class=
              "LITERAL">a.b.c.d.e.upix.com</tt> etc.</p>
            </dd>

            <dt><tt class="LITERAL">www[1-9a-ez].example.c*</tt></dt>

            <dd>
              <p>matches <tt class="LITERAL">www1.example.com</tt>,
              <tt class="LITERAL">www4.example.cc</tt>, <tt class=
              "LITERAL">wwwd.example.cy</tt>, <tt class=
              "LITERAL">wwwz.example.com</tt> etc., but <span class=
              "emphasis EMPHASIS c2">not</span> <tt class=
              "LITERAL">wwww.example.com</tt>.</p>
            </dd>
          </dl>
        </div>

        <p>While flexible, this is not the sophistication of full regular
        expression based syntax.</p>
      </div>

      <div class="SECT3">
        <h3 class="SECT3"><a name="AEN3074" id="AEN3074">8.4.2. The Path
        Pattern</a></h3>

        <p><span class="APPLICATION">Privoxy</span> uses <span class=
        "QUOTE">"modern"</span> POSIX 1003.2 <a href=
        "http://en.wikipedia.org/wiki/Regular_expressions" target=
        "_top"><span class="QUOTE">"Regular Expressions"</span></a> for
        matching the path portion (after the slash), and is thus more
        flexible.</p>

        <p>There is an <a href="appendix.html#REGEX">Appendix</a> with a
        brief quick-start into regular expressions, you also might want to
        have a look at your operating system's documentation on regular
        expressions (try <tt class="LITERAL">man re_format</tt>).</p>

        <p>Note that the path pattern is automatically left-anchored at the
        <span class="QUOTE">"/"</span>, i.e. it matches as if it would start
        with a <span class="QUOTE">"^"</span> (regular expression speak for
        the beginning of a line).</p>

        <p>Please also note that matching in the path is <span class=
        "emphasis EMPHASIS c2">CASE INSENSITIVE</span> by default, but you
        can switch to case sensitive at any point in the pattern by using the
        <span class="QUOTE">"(?-i)"</span> switch: <tt class=
        "LITERAL">www.example.com/(?-i)PaTtErN.*</tt> will match only
        documents whose path starts with <tt class="LITERAL">PaTtErN</tt> in
        <span class="emphasis EMPHASIS c2">exactly</span> this
        capitalization.</p>

        <div class="VARIABLELIST">
          <dl>
            <dt><tt class="LITERAL">.example.com/.*</tt></dt>

            <dd>
              <p>Is equivalent to just <span class=
              "QUOTE">".example.com"</span>, since any documents within that
              domain are matched with or without the <span class=
              "QUOTE">".*"</span> regular expression. This is redundant</p>
            </dd>

            <dt><tt class="LITERAL">.example.com/.*/index.html$</tt></dt>

            <dd>
              <p>Will match any page in the domain of <span class=
              "QUOTE">"example.com"</span> that is named <span class=
              "QUOTE">"index.html"</span>, and that is part of some path. For
              example, it matches <span class=
              "QUOTE">"www.example.com/testing/index.html"</span> but NOT
              <span class="QUOTE">"www.example.com/index.html"</span> because
              the regular expression called for at least two <span class=
              "QUOTE">"/'s"</span>, thus the path requirement. It also would
              match <span class=
              "QUOTE">"www.example.com/testing/index_html"</span>, because of
              the special meta-character <span class="QUOTE">"."</span>.</p>
            </dd>

            <dt><tt class="LITERAL">.example.com/(.*/)?index\.html$</tt></dt>

            <dd>
              <p>This regular expression is conditional so it will match any
              page named <span class="QUOTE">"index.html"</span> regardless
              of path which in this case can have one or more <span class=
              "QUOTE">"/'s"</span>. And this one must contain exactly
              <span class="QUOTE">".html"</span> (but does not have to end
              with that!).</p>
            </dd>

            <dt><tt class=
            "LITERAL">.example.com/(.*/)(ads|banners?|junk)</tt></dt>

            <dd>
              <p>This regular expression will match any path of <span class=
              "QUOTE">"example.com"</span> that contains any of the words
              <span class="QUOTE">"ads"</span>, <span class=
              "QUOTE">"banner"</span>, <span class="QUOTE">"banners"</span>
              (because of the <span class="QUOTE">"?"</span>) or <span class=
              "QUOTE">"junk"</span>. The path does not have to end in these
              words, just contain them.</p>
            </dd>

            <dt><tt class=
            "LITERAL">.example.com/(.*/)(ads|banners?|junk)/.*\.(jpe?g|gif|png)$</tt></dt>

            <dd>
              <p>This is very much the same as above, except now it must end
              in either <span class="QUOTE">".jpg"</span>, <span class=
              "QUOTE">".jpeg"</span>, <span class="QUOTE">".gif"</span> or
              <span class="QUOTE">".png"</span>. So this one is limited to
              common image formats.</p>
            </dd>
          </dl>
        </div>

        <p>There are many, many good examples to be found in <tt class=
        "FILENAME">default.action</tt>, and more tutorials below in <a href=
        "appendix.html#REGEX">Appendix on regular expressions</a>.</p>
      </div>

      <div class="SECT3">
        <h3 class="SECT3"><a name="TAG-PATTERN" id="TAG-PATTERN">8.4.3. The
        Tag Pattern</a></h3>

        <p>Tag patterns are used to change the applying actions based on the
        request's tags. Tags can be created with either the <a href=
        "actions-file.html#CLIENT-HEADER-TAGGER">client-header-tagger</a> or
        the <a href=
        "actions-file.html#SERVER-HEADER-TAGGER">server-header-tagger</a>
        action.</p>

        <p>Tag patterns have to start with <span class="QUOTE">"TAG:"</span>,
        so <span class="APPLICATION">Privoxy</span> can tell them apart from
        URL patterns. Everything after the colon including white space, is
        interpreted as a regular expression with path pattern syntax, except
        that tag patterns aren't left-anchored automatically (<span class=
        "APPLICATION">Privoxy</span> doesn't silently add a <span class=
        "QUOTE">"^"</span>, you have to do it yourself if you need it).</p>

        <p>To match all requests that are tagged with <span class=
        "QUOTE">"foo"</span> your pattern line should be <span class=
        "QUOTE">"TAG:^foo$"</span>, <span class="QUOTE">"TAG:foo"</span>
        would work as well, but it would also match requests whose tags
        contain <span class="QUOTE">"foo"</span> somewhere. <span class=
        "QUOTE">"TAG: foo"</span> wouldn't work as it requires white
        space.</p>

        <p>Sections can contain URL and tag patterns at the same time, but
        tag patterns are checked after the URL patterns and thus always
        overrule them, even if they are located before the URL patterns.</p>

        <p>Once a new tag is added, Privoxy checks right away if it's matched
        by one of the tag patterns and updates the action settings
        accordingly. As a result tags can be used to activate other tagger
        actions, as long as these other taggers look for headers that haven't
        already be parsed.</p>

        <p>For example you could tag client requests which use the <tt class=
        "LITERAL">POST</tt> method, then use this tag to activate another
        tagger that adds a tag if cookies are sent, and then use a block
        action based on the cookie tag. This allows the outcome of one
        action, to be input into a subsequent action. However if you'd
        reverse the position of the described taggers, and activated the
        method tagger based on the cookie tagger, no method tags would be
        created. The method tagger would look for the request line, but at
        the time the cookie tag is created, the request line has already been
        parsed.</p>

        <p>While this is a limitation you should be aware of, this kind of
        indirection is seldom needed anyway and even the example doesn't make
        too much sense.</p>
      </div>
    </div>

    <div class="SECT2">
      <h2 class="SECT2"><a name="ACTIONS" id="ACTIONS">8.5. Actions</a></h2>

      <p>All actions are disabled by default, until they are explicitly
      enabled somewhere in an actions file. Actions are turned on if preceded
      with a <span class="QUOTE">"+"</span>, and turned off if preceded with
      a <span class="QUOTE">"-"</span>. So a <tt class="LITERAL">+action</tt>
      means <span class="QUOTE">"do that action"</span>, e.g. <tt class=
      "LITERAL">+block</tt> means <span class="QUOTE">"please block URLs that
      match the following patterns"</span>, and <tt class=
      "LITERAL">-block</tt> means <span class="QUOTE">"don't block URLs that
      match the following patterns, even if <tt class="LITERAL">+block</tt>
      previously applied."</span></p>

      <p>Again, actions are invoked by placing them on a line, enclosed in
      curly braces and separated by whitespace, like in <tt class=
      "LITERAL">{+some-action -some-other-action{some-parameter}}</tt>,
      followed by a list of URL patterns, one per line, to which they apply.
      Together, the actions line and the following pattern lines make up a
      section of the actions file.</p>

      <p>Actions fall into three categories:</p>

      <ul>
        <li>
          <p>Boolean, i.e the action can only be <span class=
          "QUOTE">"enabled"</span> or <span class="QUOTE">"disabled"</span>.
          Syntax:</p>

          <table class="c4" border="0" width="90%">
            <tr>
              <td>
                <pre class="SCREEN">
  +<tt class="REPLACEABLE c5">name</tt>        # enable action <tt class=
"REPLACEABLE c5">name</tt>
  -<tt class="REPLACEABLE c5">name</tt>        # disable action <tt class=
"REPLACEABLE c5">name</tt>
</pre>
              </td>
            </tr>
          </table>

          <p>Example: <tt class="LITERAL">+handle-as-image</tt></p>
        </li>

        <li>
          <p>Parameterized, where some value is required in order to enable
          this type of action. Syntax:</p>

          <table class="c4" border="0" width="90%">
            <tr>
              <td>
                <pre class="SCREEN">
  +<tt class="REPLACEABLE c5">name</tt>{<tt class=
"REPLACEABLE c5">param</tt>}  # enable action and set parameter to <tt class=
"REPLACEABLE c5">param</tt>,
               # overwriting parameter from previous match if necessary
  -<tt class=
"REPLACEABLE c5">name</tt>         # disable action. The parameter can be omitted
</pre>
              </td>
            </tr>
          </table>

          <p>Note that if the URL matches multiple positive forms of a
          parameterized action, the last match wins, i.e. the params from
          earlier matches are simply ignored.</p>

          <p>Example: <tt class="LITERAL">+hide-user-agent{Mozilla/5.0 (X11;
          U; FreeBSD i386; en-US; rv:1.8.1.4) Gecko/20070602
          Firefox/2.0.0.4}</tt></p>
        </li>

        <li>
          <p>Multi-value. These look exactly like parameterized actions, but
          they behave differently: If the action applies multiple times to
          the same URL, but with different parameters, <span class=
          "emphasis EMPHASIS c2">all</span> the parameters from <span class=
          "emphasis EMPHASIS c2">all</span> matches are remembered. This is
          used for actions that can be executed for the same request
          repeatedly, like adding multiple headers, or filtering through
          multiple filters. Syntax:</p>

          <table class="c4" border="0" width="90%">
            <tr>
              <td>
                <pre class="SCREEN">
  +<tt class="REPLACEABLE c5">name</tt>{<tt class=
"REPLACEABLE c5">param</tt>}   # enable action and add <tt class=
"REPLACEABLE c5">param</tt> to the list of parameters
  -<tt class="REPLACEABLE c5">name</tt>{<tt class=
"REPLACEABLE c5">param</tt>}   # remove the parameter <tt class=
"REPLACEABLE c5">param</tt> from the list of parameters
                # If it was the last one left, disable the action.
  <tt class=
"REPLACEABLE c5">-name</tt>          # disable this action completely and remove all parameters from the list
</pre>
              </td>
            </tr>
          </table>

          <p>Examples: <tt class="LITERAL">+add-header{X-Fun-Header: Some
          text}</tt> and <tt class=
          "LITERAL">+filter{html-annoyances}</tt></p>
        </li>
      </ul>

      <p>If nothing is specified in any actions file, no <span class=
      "QUOTE">"actions"</span> are taken. So in this case <span class=
      "APPLICATION">Privoxy</span> would just be a normal, non-blocking,
      non-filtering proxy. You must specifically enable the privacy and
      blocking features you need (although the provided default actions files
      will give a good starting point).</p>

      <p>Later defined action sections always over-ride earlier ones of the
      same type. So exceptions to any rules you make, should come in the
      latter part of the file (or in a file that is processed later when
      using multiple actions files such as <tt class=
      "FILENAME">user.action</tt>). For multi-valued actions, the actions are
      applied in the order they are specified. Actions files are processed in
      the order they are defined in <tt class="FILENAME">config</tt> (the
      default installation has three actions files). It also quite possible
      for any given URL to match more than one <span class=
      "QUOTE">"pattern"</span> (because of wildcards and regular
      expressions), and thus to trigger more than one set of actions! Last
      match wins.</p>

      <p>The list of valid <span class="APPLICATION">Privoxy</span> actions
      are:</p>

      <div class="SECT3">
        <h4 class="SECT3"><a name="ADD-HEADER" id="ADD-HEADER">8.5.1.
        add-header</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Confuse log analysis, custom applications</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Sends a user defined HTTP header to the web server.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Multi-value.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>Any string value is possible. Validity of the defined HTTP
              headers is not checked. It is recommended that you use the
              <span class="QUOTE">"<tt class="LITERAL">X-</tt>"</span> prefix
              for custom headers.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>This action may be specified multiple times, in order to
              define multiple headers. This is rarely needed for the typical
              user. If you don't know what <span class="QUOTE">"HTTP
              headers"</span> are, you definitely don't need to worry about
              this one.</p>

              <p>Headers added by this action are not modified by other
              actions.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+add-header{X-User-Tracking: sucks}
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="BLOCK" id="BLOCK">8.5.2. block</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Block ads or other unwanted content</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Requests for URLs to which this action applies are blocked,
              i.e. the requests are trapped by <span class=
              "APPLICATION">Privoxy</span> and the requested URL is never
              retrieved, but is answered locally with a substitute page or
              image, as determined by the <tt class="LITERAL"><a href=
              "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt>,
              <tt class="LITERAL"><a href=
              "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>,
              and <tt class="LITERAL"><a href=
              "actions-file.html#HANDLE-AS-EMPTY-DOCUMENT">handle-as-empty-document</a></tt>
              actions.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>A block reason that should be given to the user.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p><span class="APPLICATION">Privoxy</span> sends a special
              <span class="QUOTE">"BLOCKED"</span> page for requests to
              blocked pages. This page contains the block reason given as
              parameter, a link to find out why the block action applies, and
              a click-through to the blocked content (the latter only if the
              force feature is available and enabled).</p>

              <p>A very important exception occurs if <span class=
              "emphasis EMPHASIS c2">both</span> <tt class=
              "LITERAL">block</tt> and <tt class="LITERAL"><a href=
              "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt>,
              apply to the same request: it will then be replaced by an
              image. If <tt class="LITERAL"><a href=
              "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>
              (see below) also applies, the type of image will be determined
              by its parameter, if not, the standard checkerboard pattern is
              sent.</p>

              <p>It is important to understand this process, in order to
              understand how <span class="APPLICATION">Privoxy</span> deals
              with ads and other unwanted content. Blocking is a core
              feature, and one upon which various other features depend.</p>

              <p>The <tt class="LITERAL"><a href=
              "actions-file.html#FILTER">filter</a></tt> action can perform a
              very similar task, by <span class="QUOTE">"blocking"</span>
              banner images and other content through rewriting the relevant
              URLs in the document's HTML source, so they don't get requested
              in the first place. Note that this is a totally different
              technique, and it's easy to confuse the two.</p>
            </dd>

            <dt>Example usage (section):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
{+block{No nasty stuff for you.}}
# Block and replace with "blocked" page
 .nasty-stuff.example.com

{+block{Doubleclick banners.} +handle-as-image}
# Block and replace with image
 .ad.doubleclick.net
 .ads.r.us/banners/

{+block{Layered ads.} +handle-as-empty-document}
# Block and then ignore
 adserver.example.net/.*\.js$
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="CHANGE-X-FORWARDED-FOR" id=
        "CHANGE-X-FORWARDED-FOR">8.5.3. change-x-forwarded-for</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Improve privacy by not forwarding the source of the request
              in the HTTP headers.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes the <span class="QUOTE">"X-Forwarded-For:"</span>
              HTTP header from the client request, or adds a new one.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <ul>
                <li>
                  <p><span class="QUOTE">"block"</span> to delete the
                  header.</p>
                </li>

                <li>
                  <p><span class="QUOTE">"add"</span> to create the header
                  (or append the client's IP address to an already existing
                  one).</p>
                </li>
              </ul>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>It is safe and recommended to use <tt class=
              "LITERAL">block</tt>.</p>

              <p>Forwarding the source address of the request may make sense
              in some multi-user setups but is also a privacy risk.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+change-x-forwarded-for{block}
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="CLIENT-HEADER-FILTER" id=
        "CLIENT-HEADER-FILTER">8.5.4. client-header-filter</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Rewrite or remove single client headers.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>All client headers to which this action applies are filtered
              on-the-fly through the specified regular expression based
              substitutions.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>The name of a client-header filter, as defined in one of the
              <a href="filter-file.html">filter files</a>.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>Client-header filters are applied to each header on its own,
              not to all at once. This makes it easier to diagnose problems,
              but on the downside you can't write filters that only change
              header x if header y's value is z. You can do that by using
              tags though.</p>

              <p>Client-header filters are executed after the other header
              actions have finished and use their output as input.</p>

              <p>If the request URL gets changed, <span class=
              "APPLICATION">Privoxy</span> will detect that and use the new
              one. This can be used to rewrite the request destination behind
              the client's back, for example to specify a Tor exit relay for
              certain requests.</p>

              <p>Please refer to the <a href="filter-file.html">filter file
              chapter</a> to learn which client-header filters are available
              by default, and how to create your own.</p>
            </dd>

            <dt>Example usage (section):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Hide Tor exit notation in Host and Referer Headers
{+client-header-filter{hide-tor-exit-notation}}
/

</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="CLIENT-HEADER-TAGGER" id=
        "CLIENT-HEADER-TAGGER">8.5.5. client-header-tagger</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Block requests based on their headers.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Client headers to which this action applies are filtered
              on-the-fly through the specified regular expression based
              substitutions, the result is used as tag.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>The name of a client-header tagger, as defined in one of the
              <a href="filter-file.html">filter files</a>.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>Client-header taggers are applied to each header on its own,
              and as the header isn't modified, each tagger <span class=
              "QUOTE">"sees"</span> the original.</p>

              <p>Client-header taggers are the first actions that are
              executed and their tags can be used to control every other
              action.</p>
            </dd>

            <dt>Example usage (section):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Tag every request with the User-Agent header
{+client-header-tagger{user-agent}}
/

# Tagging itself doesn't change the action
# settings, sections with TAG patterns do:
#
# If it's a download agent, use a different forwarding proxy,
# show the real User-Agent and make sure resume works.
{+forward-override{forward-socks5 10.0.0.2:2222 .} \
 -hide-if-modified-since      \
 -overwrite-last-modified     \
 -hide-user-agent             \
 -filter                      \
 -deanimate-gifs              \
}
TAG:^User-Agent: NetBSD-ftp/
TAG:^User-Agent: Novell ZYPP Installer
TAG:^User-Agent: RPM APT-HTTP/
TAG:^User-Agent: fetch libfetch/
TAG:^User-Agent: Ubuntu APT-HTTP/
TAG:^User-Agent: MPlayer/

</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="CONTENT-TYPE-OVERWRITE" id=
        "CONTENT-TYPE-OVERWRITE">8.5.6. content-type-overwrite</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Stop useless download menus from popping up, or change the
              browser's rendering mode</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Replaces the <span class="QUOTE">"Content-Type:"</span> HTTP
              server header.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>Any string.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>The <span class="QUOTE">"Content-Type:"</span> HTTP server
              header is used by the browser to decide what to do with the
              document. The value of this header can cause the browser to
              open a download menu instead of displaying the document by
              itself, even if the document's format is supported by the
              browser.</p>

              <p>The declared content type can also affect which rendering
              mode the browser chooses. If XHTML is delivered as <span class=
              "QUOTE">"text/html"</span>, many browsers treat it as yet
              another broken HTML document. If it is send as <span class=
              "QUOTE">"application/xml"</span>, browsers with XHTML support
              will only display it, if the syntax is correct.</p>

              <p>If you see a web site that proudly uses XHTML buttons, but
              sets <span class="QUOTE">"Content-Type: text/html"</span>, you
              can use <span class="APPLICATION">Privoxy</span> to overwrite
              it with <span class="QUOTE">"application/xml"</span> and
              validate the web master's claim inside your XHTML-supporting
              browser. If the syntax is incorrect, the browser will complain
              loudly.</p>

              <p>You can also go the opposite direction: if your browser
              prints error messages instead of rendering a document falsely
              declared as XHTML, you can overwrite the content type with
              <span class="QUOTE">"text/html"</span> and have it rendered as
              broken HTML document.</p>

              <p>By default <tt class="LITERAL">content-type-overwrite</tt>
              only replaces <span class="QUOTE">"Content-Type:"</span>
              headers that look like some kind of text. If you want to
              overwrite it unconditionally, you have to combine it with
              <tt class="LITERAL"><a href=
              "actions-file.html#FORCE-TEXT-MODE">force-text-mode</a></tt>.
              This limitation exists for a reason, think twice before
              circumventing it.</p>

              <p>Most of the time it's easier to replace this action with a
              custom <tt class="LITERAL"><a href=
              "actions-file.html#SERVER-HEADER-FILTER">server-header
              filter</a></tt>. It allows you to activate it for every
              document of a certain site and it will still only replace the
              content types you aimed at.</p>

              <p>Of course you can apply <tt class=
              "LITERAL">content-type-overwrite</tt> to a whole site and then
              make URL based exceptions, but it's a lot more work to get the
              same precision.</p>
            </dd>

            <dt>Example usage (sections):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Check if www.example.net/ really uses valid XHTML
{ +content-type-overwrite{application/xml} }
www.example.net/

# but leave the content type unmodified if the URL looks like a style sheet
{-content-type-overwrite}
www.example.net/.*\.css$
www.example.net/.*style
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="CRUNCH-CLIENT-HEADER" id=
        "CRUNCH-CLIENT-HEADER">8.5.7. crunch-client-header</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Remove a client header <span class=
              "APPLICATION">Privoxy</span> has no dedicated action for.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes every header sent by the client that contains the
              string the user supplied as parameter.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>Any string.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>This action allows you to block client headers for which no
              dedicated <span class="APPLICATION">Privoxy</span> action
              exists. <span class="APPLICATION">Privoxy</span> will remove
              every client header that contains the string you supplied as
              parameter.</p>

              <p>Regular expressions are <span class=
              "emphasis EMPHASIS c2">not supported</span> and you can't use
              this action to block different headers in the same request,
              unless they contain the same string.</p>

              <p><tt class="LITERAL">crunch-client-header</tt> is only meant
              for quick tests. If you have to block several different
              headers, or only want to modify parts of them, you should use a
              <tt class="LITERAL"><a href=
              "actions-file.html#CLIENT-HEADER-FILTER">client-header
              filter</a></tt>.</p>

              <div class="WARNING">
                <table class="WARNING" border="1" width="90%">
                  <tr>
                    <td class="c6" align="center">Warning</td>
                  </tr>

                  <tr>
                    <td align="left">
                      <p>Don't block any header without understanding the
                      consequences.</p>
                    </td>
                  </tr>
                </table>
              </div>
            </dd>

            <dt>Example usage (section):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Block the non-existent "Privacy-Violation:" client header
{ +crunch-client-header{Privacy-Violation:} }
/

</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="CRUNCH-IF-NONE-MATCH" id=
        "CRUNCH-IF-NONE-MATCH">8.5.8. crunch-if-none-match</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Prevent yet another way to track the user's steps between
              sessions.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes the <span class="QUOTE">"If-None-Match:"</span> HTTP
              client header.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Boolean.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>N/A</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>Removing the <span class="QUOTE">"If-None-Match:"</span>
              HTTP client header is useful for filter testing, where you want
              to force a real reload instead of getting status code
              <span class="QUOTE">"304"</span> which would cause the browser
              to use a cached copy of the page.</p>

              <p>It is also useful to make sure the header isn't used as a
              cookie replacement (unlikely but possible).</p>

              <p>Blocking the <span class="QUOTE">"If-None-Match:"</span>
              header shouldn't cause any caching problems, as long as the
              <span class="QUOTE">"If-Modified-Since:"</span> header isn't
              blocked or missing as well.</p>

              <p>It is recommended to use this action together with
              <tt class="LITERAL"><a href=
              "actions-file.html#HIDE-IF-MODIFIED-SINCE">hide-if-modified-since</a></tt>
              and <tt class="LITERAL"><a href=
              "actions-file.html#OVERWRITE-LAST-MODIFIED">overwrite-last-modified</a></tt>.</p>
            </dd>

            <dt>Example usage (section):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Let the browser revalidate cached documents but don't
# allow the server to use the revalidation headers for user tracking.
{+hide-if-modified-since{-60} \
 +overwrite-last-modified{randomize} \
 +crunch-if-none-match}
/
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="CRUNCH-INCOMING-COOKIES" id=
        "CRUNCH-INCOMING-COOKIES">8.5.9. crunch-incoming-cookies</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Prevent the web server from setting HTTP cookies on your
              system</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes any <span class="QUOTE">"Set-Cookie:"</span> HTTP
              headers from server replies.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Boolean.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>N/A</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>This action is only concerned with <span class=
              "emphasis EMPHASIS c2">incoming</span> HTTP cookies. For
              <span class="emphasis EMPHASIS c2">outgoing</span> HTTP
              cookies, use <tt class="LITERAL"><a href=
              "actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt>.
              Use <span class="emphasis EMPHASIS c2">both</span> to disable
              HTTP cookies completely.</p>

              <p>It makes <span class="emphasis EMPHASIS c2">no sense at
              all</span> to use this action in conjunction with the
              <tt class="LITERAL"><a href=
              "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a></tt>
              action, since it would prevent the session cookies from being
              set. See also <tt class="LITERAL"><a href=
              "actions-file.html#FILTER-CONTENT-COOKIES">filter-content-cookies</a></tt>.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+crunch-incoming-cookies
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="CRUNCH-SERVER-HEADER" id=
        "CRUNCH-SERVER-HEADER">8.5.10. crunch-server-header</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Remove a server header <span class=
              "APPLICATION">Privoxy</span> has no dedicated action for.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes every header sent by the server that contains the
              string the user supplied as parameter.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>Any string.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>This action allows you to block server headers for which no
              dedicated <span class="APPLICATION">Privoxy</span> action
              exists. <span class="APPLICATION">Privoxy</span> will remove
              every server header that contains the string you supplied as
              parameter.</p>

              <p>Regular expressions are <span class=
              "emphasis EMPHASIS c2">not supported</span> and you can't use
              this action to block different headers in the same request,
              unless they contain the same string.</p>

              <p><tt class="LITERAL">crunch-server-header</tt> is only meant
              for quick tests. If you have to block several different
              headers, or only want to modify parts of them, you should use a
              custom <tt class="LITERAL"><a href=
              "actions-file.html#SERVER-HEADER-FILTER">server-header
              filter</a></tt>.</p>

              <div class="WARNING">
                <table class="WARNING" border="1" width="90%">
                  <tr>
                    <td class="c6" align="center">Warning</td>
                  </tr>

                  <tr>
                    <td align="left">
                      <p>Don't block any header without understanding the
                      consequences.</p>
                    </td>
                  </tr>
                </table>
              </div>
            </dd>

            <dt>Example usage (section):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Crunch server headers that try to prevent caching
{ +crunch-server-header{no-cache} }
/
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="CRUNCH-OUTGOING-COOKIES" id=
        "CRUNCH-OUTGOING-COOKIES">8.5.11. crunch-outgoing-cookies</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Prevent the web server from reading any HTTP cookies from
              your system</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes any <span class="QUOTE">"Cookie:"</span> HTTP
              headers from client requests.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Boolean.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>N/A</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>This action is only concerned with <span class=
              "emphasis EMPHASIS c2">outgoing</span> HTTP cookies. For
              <span class="emphasis EMPHASIS c2">incoming</span> HTTP
              cookies, use <tt class="LITERAL"><a href=
              "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt>.
              Use <span class="emphasis EMPHASIS c2">both</span> to disable
              HTTP cookies completely.</p>

              <p>It makes <span class="emphasis EMPHASIS c2">no sense at
              all</span> to use this action in conjunction with the
              <tt class="LITERAL"><a href=
              "actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a></tt>
              action, since it would prevent the session cookies from being
              read.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+crunch-outgoing-cookies
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="DEANIMATE-GIFS" id=
        "DEANIMATE-GIFS">8.5.12. deanimate-gifs</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Stop those annoying, distracting animated GIF images.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>De-animate GIF animations, i.e. reduce them to their first
              or last image.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p><span class="QUOTE">"last"</span> or <span class=
              "QUOTE">"first"</span></p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>This will also shrink the images considerably (in bytes, not
              pixels!). If the option <span class="QUOTE">"first"</span> is
              given, the first frame of the animation is used as the
              replacement. If <span class="QUOTE">"last"</span> is given, the
              last frame of the animation is used instead, which probably
              makes more sense for most banner animations, but also has the
              risk of not showing the entire last frame (if it is only a
              delta to an earlier frame).</p>

              <p>You can safely use this action with patterns that will also
              match non-GIF objects, because no attempt will be made at
              anything that doesn't look like a GIF.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+deanimate-gifs{last}
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="DOWNGRADE-HTTP-VERSION" id=
        "DOWNGRADE-HTTP-VERSION">8.5.13. downgrade-http-version</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Work around (very rare) problems with HTTP/1.1</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Downgrades HTTP/1.1 client requests and server replies to
              HTTP/1.0.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Boolean.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>N/A</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>This is a left-over from the time when <span class=
              "APPLICATION">Privoxy</span> didn't support important HTTP/1.1
              features well. It is left here for the unlikely case that you
              experience HTTP/1.1-related problems with some server out
              there.</p>

              <p>Note that enabling this action is only a workaround. It
              should not be enabled for sites that work without it. While it
              shouldn't break any pages, it has an (usually negative)
              performance impact.</p>

              <p>If you come across a site where enabling this action helps,
              please report it, so the cause of the problem can be analyzed.
              If the problem turns out to be caused by a bug in <span class=
              "APPLICATION">Privoxy</span> it should be fixed so the
              following release works without the work around.</p>
            </dd>

            <dt>Example usage (section):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
{+downgrade-http-version}
problem-host.example.com
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="FAST-REDIRECTS" id=
        "FAST-REDIRECTS">8.5.14. fast-redirects</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Fool some click-tracking scripts and speed up indirect
              links.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Detects redirection URLs and redirects the browser without
              contacting the redirection server first.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <ul>
                <li>
                  <p><span class="QUOTE">"simple-check"</span> to just search
                  for the string <span class="QUOTE">"http://"</span> to
                  detect redirection URLs.</p>
                </li>

                <li>
                  <p><span class="QUOTE">"check-decoded-url"</span> to decode
                  URLs (if necessary) before searching for redirection
                  URLs.</p>
                </li>
              </ul>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>Many sites, like yahoo.com, don't just link to other sites.
              Instead, they will link to some script on their own servers,
              giving the destination as a parameter, which will then redirect
              you to the final target. URLs resulting from this scheme
              typically look like: <span class=
              "QUOTE">"http://www.example.org/click-tracker.cgi?target=http%3a//www.example.net/"</span>.</p>

              <p>Sometimes, there are even multiple consecutive redirects
              encoded in the URL. These redirections via scripts make your
              web browsing more traceable, since the server from which you
              follow such a link can see where you go to. Apart from that,
              valuable bandwidth and time is wasted, while your browser asks
              the server for one redirect after the other. Plus, it feeds the
              advertisers.</p>

              <p>This feature is currently not very smart and is scheduled
              for improvement. If it is enabled by default, you will have to
              create some exceptions to this action. It can lead to failures
              in several ways:</p>

              <p>Not every URLs with other URLs as parameters is evil. Some
              sites offer a real service that requires this information to
              work. For example a validation service needs to know, which
              document to validate. <tt class="LITERAL">fast-redirects</tt>
              assumes that every URL parameter that looks like another URL is
              a redirection target, and will always redirect to the last one.
              Most of the time the assumption is correct, but if it isn't,
              the user gets redirected anyway.</p>

              <p>Another failure occurs if the URL contains other parameters
              after the URL parameter. The URL: <span class=
              "QUOTE">"http://www.example.org/?redirect=http%3a//www.example.net/&amp;foo=bar"</span>.
              contains the redirection URL <span class=
              "QUOTE">"http://www.example.net/"</span>, followed by another
              parameter. <tt class="LITERAL">fast-redirects</tt> doesn't know
              that and will cause a redirect to <span class=
              "QUOTE">"http://www.example.net/&amp;foo=bar"</span>. Depending
              on the target server configuration, the parameter will be
              silently ignored or lead to a <span class="QUOTE">"page not
              found"</span> error. You can prevent this problem by first
              using the <tt class="LITERAL"><a href=
              "actions-file.html#REDIRECT">redirect</a></tt> action to remove
              the last part of the URL, but it requires a little effort.</p>

              <p>To detect a redirection URL, <tt class=
              "LITERAL">fast-redirects</tt> only looks for the string
              <span class="QUOTE">"http://"</span>, either in plain text
              (invalid but often used) or encoded as <span class=
              "QUOTE">"http%3a//"</span>. Some sites use their own URL
              encoding scheme, encrypt the address of the target server or
              replace it with a database id. In theses cases <tt class=
              "LITERAL">fast-redirects</tt> is fooled and the request reaches
              the redirection server where it probably gets logged.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
 { +fast-redirects{simple-check} }
   one.example.com

 { +fast-redirects{check-decoded-url} }
   another.example.com/testing
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="FILTER" id="FILTER">8.5.15.
        filter</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Get rid of HTML and JavaScript annoyances, banner
              advertisements (by size), do fun text replacements, add
              personalized effects, etc.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>All instances of text-based type, most notably HTML and
              JavaScript, to which this action applies, can be filtered
              on-the-fly through the specified regular expression based
              substitutions. (Note: as of version 3.0.3 plain text documents
              are exempted from filtering, because web servers often use the
              <tt class="LITERAL">text/plain</tt> MIME type for all files
              whose type they don't know.)</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>The name of a content filter, as defined in the <a href=
              "filter-file.html">filter file</a>. Filters can be defined in
              one or more files as defined by the <tt class=
              "LITERAL"><a href="config.html#FILTERFILE">filterfile</a></tt>
              option in the <a href="config.html">config file</a>. <tt class=
              "FILENAME">default.filter</tt> is the collection of filters
              supplied by the developers. Locally defined filters should go
              in their own file, such as <tt class=
              "FILENAME">user.filter</tt>.</p>

              <p>When used in its negative form, and without parameters,
              <span class="emphasis EMPHASIS c2">all</span> filtering is
              completely disabled.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>For your convenience, there are a number of pre-defined
              filters available in the distribution filter file that you can
              use. See the examples below for a list.</p>

              <p>Filtering requires buffering the page content, which may
              appear to slow down page rendering since nothing is displayed
              until all content has passed the filters. (The total time until
              the page is completely rendered doesn't change much, but it may
              be perceived as slower since the page is not incrementally
              displayed.) This effect will be more noticeable on slower
              connections.</p>

              <p><span class="QUOTE">"Rolling your own"</span> filters
              requires a knowledge of <a href=
              "http://en.wikipedia.org/wiki/Regular_expressions" target=
              "_top"><span class="QUOTE">"Regular Expressions"</span></a> and
              <a href="http://en.wikipedia.org/wiki/Html" target=
              "_top"><span class="QUOTE">"HTML"</span></a>. This is very
              powerful feature, and potentially very intrusive. Filters
              should be used with caution, and where an equivalent
              <span class="QUOTE">"action"</span> is not available.</p>

              <p>The amount of data that can be filtered is limited to the
              <tt class="LITERAL"><a href=
              "config.html#BUFFER-LIMIT">buffer-limit</a></tt> option in the
              main <a href="config.html">config file</a>. The default is 4096
              KB (4 Megs). Once this limit is exceeded, the buffered data,
              and all pending data, is passed through unfiltered.</p>

              <p>Inappropriate MIME types, such as zipped files, are not
              filtered at all. (Again, only text-based types except plain
              text). Encrypted SSL data (from HTTPS servers) cannot be
              filtered either, since this would violate the integrity of the
              secure transaction. In some situations it might be necessary to
              protect certain text, like source code, from filtering by
              defining appropriate <tt class="LITERAL">-filter</tt>
              exceptions.</p>

              <p>Compressed content can't be filtered either, but if
              <span class="APPLICATION">Privoxy</span> is compiled with zlib
              support and a supported compression algorithm is used (gzip or
              deflate), <span class="APPLICATION">Privoxy</span> can first
              decompress the content and then filter it.</p>

              <p>If you use a <span class="APPLICATION">Privoxy</span>
              version without zlib support, but want filtering to work on as
              much documents as possible, even those that would normally be
              sent compressed, you must use the <tt class="LITERAL"><a href=
              "actions-file.html#PREVENT-COMPRESSION">prevent-compression</a></tt>
              action in conjunction with <tt class="LITERAL">filter</tt>.</p>

              <p>Content filtering can achieve some of the same effects as
              the <tt class="LITERAL"><a href=
              "actions-file.html#BLOCK">block</a></tt> action, i.e. it can be
              used to block ads and banners. But the mechanism works quite
              differently. One effective use, is to block ad banners based on
              their size (see below), since many of these seem to be somewhat
              standardized.</p>

              <p><a href="contact.html">Feedback</a> with suggestions for new
              or improved filters is particularly welcome!</p>

              <p>The below list has only the names and a one-line description
              of each predefined filter. There are <a href=
              "filter-file.html#PREDEFINED-FILTERS">more verbose
              explanations</a> of what these filters do in the <a href=
              "filter-file.html">filter file chapter</a>.</p>
            </dd>

            <dt>Example usage (with filters from the distribution <tt class=
            "FILENAME">default.filter</tt> file). See <a href=
            "filter-file.html#PREDEFINED-FILTERS">the Predefined Filters
            section</a> for more explanation on each:</dt>

            <dd>
              <p><a name="FILTER-JS-ANNOYANCES" id=
              "FILTER-JS-ANNOYANCES"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{js-annoyances}       # Get rid of particularly annoying JavaScript abuse.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-JS-EVENTS" id="FILTER-JS-EVENTS"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{js-events}           # Kill all JS event bindings and timers (Radically destructive! Only for extra nasty sites).
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-HTML-ANNOYANCES" id=
              "FILTER-HTML-ANNOYANCES"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{html-annoyances}     # Get rid of particularly annoying HTML abuse.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-CONTENT-COOKIES" id=
              "FILTER-CONTENT-COOKIES"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{content-cookies}     # Kill cookies that come in the HTML or JS content.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-REFRESH-TAGS" id=
              "FILTER-REFRESH-TAGS"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{refresh-tags}        # Kill automatic refresh tags (for dial-on-demand setups).
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-UNSOLICITED-POPUPS" id=
              "FILTER-UNSOLICITED-POPUPS"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{unsolicited-popups}  # Disable only unsolicited pop-up windows. Useful if your browser lacks this ability.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-ALL-POPUPS" id="FILTER-ALL-POPUPS"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{all-popups}          # Kill all popups in JavaScript and HTML. Useful if your browser lacks this ability.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-IMG-REORDER" id=
              "FILTER-IMG-REORDER"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{img-reorder}         # Reorder attributes in &lt;img&gt; tags to make the banners-by-* filters more effective.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-BANNERS-BY-SIZE" id=
              "FILTER-BANNERS-BY-SIZE"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{banners-by-size}     # Kill banners by size.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-BANNERS-BY-LINK" id=
              "FILTER-BANNERS-BY-LINK"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{banners-by-link}     # Kill banners by their links to known clicktrackers.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-WEBBUGS" id="FILTER-WEBBUGS"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{webbugs}             # Squish WebBugs (1x1 invisible GIFs used for user tracking).
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-TINY-TEXTFORMS" id=
              "FILTER-TINY-TEXTFORMS"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{tiny-textforms}      # Extend those tiny textareas up to 40x80 and kill the hard wrap.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-JUMPING-WINDOWS" id=
              "FILTER-JUMPING-WINDOWS"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{jumping-windows}     # Prevent windows from resizing and moving themselves.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-FRAMESET-BORDERS" id=
              "FILTER-FRAMESET-BORDERS"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{frameset-borders}    # Give frames a border and make them resizable.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-DEMORONIZER" id=
              "FILTER-DEMORONIZER"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{demoronizer}         # Fix MS's non-standard use of standard charsets.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-SHOCKWAVE-FLASH" id=
              "FILTER-SHOCKWAVE-FLASH"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{shockwave-flash}     # Kill embedded Shockwave Flash objects.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-QUICKTIME-KIOSKMODE" id=
              "FILTER-QUICKTIME-KIOSKMODE"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{quicktime-kioskmode} # Make Quicktime movies saveable.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-FUN" id="FILTER-FUN"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{fun}                 # Text replacements for subversive browsing fun!
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-CRUDE-PARENTAL" id=
              "FILTER-CRUDE-PARENTAL"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{crude-parental}      # Crude parental filtering. Note that this filter doesn't work reliably.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-IE-EXPLOITS" id=
              "FILTER-IE-EXPLOITS"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{ie-exploits}         # Disable some known Internet Explorer bug exploits.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-SITE-SPECIFICS" id=
              "FILTER-SITE-SPECIFICS"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{site-specifics}      # Cure for site-specific problems. Don't apply generally!
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-NO-PING" id="FILTER-NO-PING"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{no-ping}             # Removes non-standard ping attributes in &lt;a&gt; and &lt;area&gt; tags.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-GOOGLE" id="FILTER-GOOGLE"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{google}              # CSS-based block for Google text ads. Also removes a width limitation and the toolbar advertisement.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-YAHOO" id="FILTER-YAHOO"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{yahoo}               # CSS-based block for Yahoo text ads. Also removes a width limitation.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-MSN" id="FILTER-MSN"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{msn}                 # CSS-based block for MSN text ads. Also removes tracking URLs and a width limitation.
</pre>
                  </td>
                </tr>
              </table>

              <p><a name="FILTER-BLOGSPOT" id="FILTER-BLOGSPOT"></a></p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+filter{blogspot}            # Cleans up some Blogspot blogs. Read the fine print before using this.
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="FORCE-TEXT-MODE" id=
        "FORCE-TEXT-MODE">8.5.16. force-text-mode</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Force <span class="APPLICATION">Privoxy</span> to treat a
              document as if it was in some kind of <span class=
              "emphasis EMPHASIS c2">text</span> format.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Declares a document as text, even if the <span class=
              "QUOTE">"Content-Type:"</span> isn't detected as such.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Boolean.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>N/A</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>As explained <tt class="LITERAL"><a href=
              "actions-file.html#FILTER">above</a></tt>, <span class=
              "APPLICATION">Privoxy</span> tries to only filter files that
              are in some kind of text format. The same restrictions apply to
              <tt class="LITERAL"><a href=
              "actions-file.html#CONTENT-TYPE-OVERWRITE">content-type-overwrite</a></tt>.
              <tt class="LITERAL">force-text-mode</tt> declares a document as
              text, without looking at the <span class=
              "QUOTE">"Content-Type:"</span> first.</p>

              <div class="WARNING">
                <table class="WARNING" border="1" width="90%">
                  <tr>
                    <td class="c6" align="center">Warning</td>
                  </tr>

                  <tr>
                    <td align="left">
                      <p>Think twice before activating this action. Filtering
                      binary data with regular expressions can cause file
                      damage.</p>
                    </td>
                  </tr>
                </table>
              </div>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+force-text-mode

</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="FORWARD-OVERRIDE" id=
        "FORWARD-OVERRIDE">8.5.17. forward-override</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Change the forwarding settings based on User-Agent or
              request origin</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Overrules the forward directives in the configuration
              file.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Multi-value.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <ul>
                <li>
                  <p><span class="QUOTE">"forward ."</span> to use a direct
                  connection without any additional proxies.</p>
                </li>

                <li>
                  <p><span class="QUOTE">"forward 127.0.0.1:8123"</span> to
                  use the HTTP proxy listening at 127.0.0.1 port 8123.</p>
                </li>

                <li>
                  <p><span class="QUOTE">"forward-socks4a 127.0.0.1:9050
                  ."</span> to use the socks4a proxy listening at 127.0.0.1
                  port 9050. Replace <span class=
                  "QUOTE">"forward-socks4a"</span> with <span class=
                  "QUOTE">"forward-socks4"</span> to use a socks4 connection
                  (with local DNS resolution) instead, use <span class=
                  "QUOTE">"forward-socks5"</span> for socks5 connections
                  (with remote DNS resolution).</p>
                </li>

                <li>
                  <p><span class="QUOTE">"forward-socks4a 127.0.0.1:9050
                  proxy.example.org:8000"</span> to use the socks4a proxy
                  listening at 127.0.0.1 port 9050 to reach the HTTP proxy
                  listening at proxy.example.org port 8000. Replace
                  <span class="QUOTE">"forward-socks4a"</span> with
                  <span class="QUOTE">"forward-socks4"</span> to use a socks4
                  connection (with local DNS resolution) instead, use
                  <span class="QUOTE">"forward-socks5"</span> for socks5
                  connections (with remote DNS resolution).</p>
                </li>
              </ul>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>This action takes parameters similar to the <a href=
              "config.html#FORWARDING">forward</a> directives in the
              configuration file, but without the URL pattern. It can be used
              as replacement, but normally it's only used in cases where
              matching based on the request URL isn't sufficient.</p>

              <div class="WARNING">
                <table class="WARNING" border="1" width="90%">
                  <tr>
                    <td class="c6" align="center">Warning</td>
                  </tr>

                  <tr>
                    <td align="left">
                      <p>Please read the description for the <a href=
                      "config.html#FORWARDING">forward</a> directives before
                      using this action. Forwarding to the wrong people will
                      reduce your privacy and increase the chances of
                      man-in-the-middle attacks.</p>

                      <p>If the ports are missing or invalid, default values
                      will be used. This might change in the future and you
                      shouldn't rely on it. Otherwise incorrect syntax causes
                      Privoxy to exit.</p>

                      <p>Use the <a href=
                      "http://config.privoxy.org/show-url-info" target=
                      "_top">show-url-info CGI page</a> to verify that your
                      forward settings do what you thought the do.</p>
                    </td>
                  </tr>
                </table>
              </div>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Always use direct connections for requests previously tagged as
# <span class="QUOTE">"User-Agent: fetch libfetch/2.0"</span> and make sure
# resuming downloads continues to work.
# This way you can continue to use Tor for your normal browsing,
# without overloading the Tor network with your FreeBSD ports updates
# or downloads of bigger files like ISOs.
# Note that HTTP headers are easy to fake and therefore their
# values are as (un)trustworthy as your clients and users.
{+forward-override{forward .} \
 -hide-if-modified-since      \
 -overwrite-last-modified     \
}
TAG:^User-Agent: fetch libfetch/2\.0$

</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="HANDLE-AS-EMPTY-DOCUMENT" id=
        "HANDLE-AS-EMPTY-DOCUMENT">8.5.18. handle-as-empty-document</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Mark URLs that should be replaced by empty documents
              <span class="emphasis EMPHASIS c2">if they get
              blocked</span></p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>This action alone doesn't do anything noticeable. It just
              marks URLs. If the <tt class="LITERAL"><a href=
              "actions-file.html#BLOCK">block</a></tt> action <span class=
              "emphasis EMPHASIS c2">also applies</span>, the presence or
              absence of this mark decides whether an HTML <span class=
              "QUOTE">"BLOCKED"</span> page, or an empty document will be
              sent to the client as a substitute for the blocked content. The
              <span class="emphasis EMPHASIS c2">empty</span> document isn't
              literally empty, but actually contains a single space.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Boolean.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>N/A</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>Some browsers complain about syntax errors if JavaScript
              documents are blocked with <span class=
              "APPLICATION">Privoxy's</span> default HTML page; this option
              can be used to silence them. And of course this action can also
              be used to eliminate the <span class=
              "APPLICATION">Privoxy</span> BLOCKED message in frames.</p>

              <p>The content type for the empty document can be specified
              with <tt class="LITERAL"><a href=
              "actions-file.html#CONTENT-TYPE-OVERWRITE">content-type-overwrite{}</a></tt>,
              but usually this isn't necessary.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Block all documents on example.org that end with ".js",
# but send an empty document instead of the usual HTML message.
{+block{Blocked JavaScript} +handle-as-empty-document}
example.org/.*\.js$

</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="HANDLE-AS-IMAGE" id=
        "HANDLE-AS-IMAGE">8.5.19. handle-as-image</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Mark URLs as belonging to images (so they'll be replaced by
              images <span class="emphasis EMPHASIS c2">if they do get
              blocked</span>, rather than HTML pages)</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>This action alone doesn't do anything noticeable. It just
              marks URLs as images. If the <tt class="LITERAL"><a href=
              "actions-file.html#BLOCK">block</a></tt> action <span class=
              "emphasis EMPHASIS c2">also applies</span>, the presence or
              absence of this mark decides whether an HTML <span class=
              "QUOTE">"blocked"</span> page, or a replacement image (as
              determined by the <tt class="LITERAL"><a href=
              "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>
              action) will be sent to the client as a substitute for the
              blocked content.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Boolean.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>N/A</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>The below generic example section is actually part of
              <tt class="FILENAME">default.action</tt>. It marks all URLs
              with well-known image file name extensions as images and should
              be left intact.</p>

              <p>Users will probably only want to use the handle-as-image
              action in conjunction with <tt class="LITERAL"><a href=
              "actions-file.html#BLOCK">block</a></tt>, to block sources of
              banners, whose URLs don't reflect the file type, like in the
              second example section.</p>

              <p>Note that you cannot treat HTML pages as images in most
              cases. For instance, (in-line) ad frames require an HTML page
              to be sent, or they won't display properly. Forcing <tt class=
              "LITERAL">handle-as-image</tt> in this situation will not
              replace the ad frame with an image, but lead to error
              messages.</p>
            </dd>

            <dt>Example usage (sections):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Generic image extensions:
#
{+handle-as-image}
/.*\.(gif|jpg|jpeg|png|bmp|ico)$

# These don't look like images, but they're banners and should be
# blocked as images:
#
{+block{Nasty banners.} +handle-as-image}
nasty-banner-server.example.com/junk.cgi\?output=trash
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="HIDE-ACCEPT-LANGUAGE" id=
        "HIDE-ACCEPT-LANGUAGE">8.5.20. hide-accept-language</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Pretend to use different language settings.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes or replaces the <span class=
              "QUOTE">"Accept-Language:"</span> HTTP header in client
              requests.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>Keyword: <span class="QUOTE">"block"</span>, or any user
              defined value.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>Faking the browser's language settings can be useful to make
              a foreign User-Agent set with <tt class="LITERAL"><a href=
              "actions-file.html#HIDE-USER-AGENT">hide-user-agent</a></tt>
              more believable.</p>

              <p>However some sites with content in different languages check
              the <span class="QUOTE">"Accept-Language:"</span> to decide
              which one to take by default. Sometimes it isn't possible to
              later switch to another language without changing the
              <span class="QUOTE">"Accept-Language:"</span> header first.</p>

              <p>Therefore it's a good idea to either only change the
              <span class="QUOTE">"Accept-Language:"</span> header to
              languages you understand, or to languages that aren't wide
              spread.</p>

              <p>Before setting the <span class=
              "QUOTE">"Accept-Language:"</span> header to a rare language,
              you should consider that it helps to make your requests unique
              and thus easier to trace. If you don't plan to change this
              header frequently, you should stick to a common language.</p>
            </dd>

            <dt>Example usage (section):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Pretend to use Canadian language settings.
{+hide-accept-language{en-ca} \
+hide-user-agent{Mozilla/5.0 (X11; U; OpenBSD i386; en-CA; rv:1.8.0.4) Gecko/20060628 Firefox/1.5.0.4} \
}
/
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="HIDE-CONTENT-DISPOSITION" id=
        "HIDE-CONTENT-DISPOSITION">8.5.21. hide-content-disposition</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Prevent download menus for content you prefer to view inside
              the browser.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes or replaces the <span class=
              "QUOTE">"Content-Disposition:"</span> HTTP header set by some
              servers.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>Keyword: <span class="QUOTE">"block"</span>, or any user
              defined value.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>Some servers set the <span class=
              "QUOTE">"Content-Disposition:"</span> HTTP header for documents
              they assume you want to save locally before viewing them. The
              <span class="QUOTE">"Content-Disposition:"</span> header
              contains the file name the browser is supposed to use by
              default.</p>

              <p>In most browsers that understand this header, it makes it
              impossible to <span class="emphasis EMPHASIS c2">just
              view</span> the document, without downloading it first, even if
              it's just a simple text file or an image.</p>

              <p>Removing the <span class=
              "QUOTE">"Content-Disposition:"</span> header helps to prevent
              this annoyance, but some browsers additionally check the
              <span class="QUOTE">"Content-Type:"</span> header, before they
              decide if they can display a document without saving it first.
              In these cases, you have to change this header as well, before
              the browser stops displaying download menus.</p>

              <p>It is also possible to change the server's file name
              suggestion to another one, but in most cases it isn't worth the
              time to set it up.</p>

              <p>This action will probably be removed in the future, use
              server-header filters instead.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Disarm the download link in Sourceforge's patch tracker
{ -filter \
 +content-type-overwrite{text/plain}\
 +hide-content-disposition{block} }
 .sourceforge.net/tracker/download\.php
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="HIDE-IF-MODIFIED-SINCE" id=
        "HIDE-IF-MODIFIED-SINCE">8.5.22. hide-if-modified-since</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Prevent yet another way to track the user's steps between
              sessions.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes the <span class="QUOTE">"If-Modified-Since:"</span>
              HTTP client header or modifies its value.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>Keyword: <span class="QUOTE">"block"</span>, or a user
              defined value that specifies a range of hours.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>Removing this header is useful for filter testing, where you
              want to force a real reload instead of getting status code
              <span class="QUOTE">"304"</span>, which would cause the browser
              to use a cached copy of the page.</p>

              <p>Instead of removing the header, <tt class=
              "LITERAL">hide-if-modified-since</tt> can also add or subtract
              a random amount of time to/from the header's value. You specify
              a range of minutes where the random factor should be chosen
              from and <span class="APPLICATION">Privoxy</span> does the
              rest. A negative value means subtracting, a positive value
              adding.</p>

              <p>Randomizing the value of the <span class=
              "QUOTE">"If-Modified-Since:"</span> makes it less likely that
              the server can use the time as a cookie replacement, but you
              will run into caching problems if the random range is too
              high.</p>

              <p>It is a good idea to only use a small negative value and let
              <tt class="LITERAL"><a href=
              "actions-file.html#OVERWRITE-LAST-MODIFIED">overwrite-last-modified</a></tt>
              handle the greater changes.</p>

              <p>It is also recommended to use this action together with
              <tt class="LITERAL"><a href=
              "actions-file.html#CRUNCH-IF-NONE-MATCH">crunch-if-none-match</a></tt>,
              otherwise it's more or less pointless.</p>
            </dd>

            <dt>Example usage (section):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Let the browser revalidate but make tracking based on the time less likely.
{+hide-if-modified-since{-60} \
 +overwrite-last-modified{randomize} \
 +crunch-if-none-match}
/
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="HIDE-FROM-HEADER" id=
        "HIDE-FROM-HEADER">8.5.23. hide-from-header</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Keep your (old and ill) browser from telling web servers
              your email address</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes any existing <span class="QUOTE">"From:"</span> HTTP
              header, or replaces it with the specified string.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>Keyword: <span class="QUOTE">"block"</span>, or any user
              defined value.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>The keyword <span class="QUOTE">"block"</span> will
              completely remove the header (not to be confused with the
              <tt class="LITERAL"><a href=
              "actions-file.html#BLOCK">block</a></tt> action).</p>

              <p>Alternately, you can specify any value you prefer to be sent
              to the web server. If you do, it is a matter of fairness not to
              use any address that is actually used by a real person.</p>

              <p>This action is rarely needed, as modern web browsers don't
              send <span class="QUOTE">"From:"</span> headers anymore.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+hide-from-header{block}
</pre>
                  </td>
                </tr>
              </table>or

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+hide-from-header{spam-me-senseless@sittingduck.example.com}
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="HIDE-REFERRER" id="HIDE-REFERRER">8.5.24.
        hide-referrer</a></h4><a name="HIDE-REFERER" id="HIDE-REFERER"></a>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Conceal which link you followed to get to a particular
              site</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes the <span class="QUOTE">"Referer:"</span> (sic) HTTP
              header from the client request, or replaces it with a forged
              one.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <ul>
                <li>
                  <p><span class="QUOTE">"conditional-block"</span> to delete
                  the header completely if the host has changed.</p>
                </li>

                <li>
                  <p><span class="QUOTE">"conditional-forge"</span> to forge
                  the header if the host has changed.</p>
                </li>

                <li>
                  <p><span class="QUOTE">"block"</span> to delete the header
                  unconditionally.</p>
                </li>

                <li>
                  <p><span class="QUOTE">"forge"</span> to pretend to be
                  coming from the homepage of the server we are talking
                  to.</p>
                </li>

                <li>
                  <p>Any other string to set a user defined referrer.</p>
                </li>
              </ul>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p><tt class="LITERAL">conditional-block</tt> is the only
              parameter, that isn't easily detected in the server's log file.
              If it blocks the referrer, the request will look like the
              visitor used a bookmark or typed in the address directly.</p>

              <p>Leaving the referrer unmodified for requests on the same
              host allows the server owner to see the visitor's <span class=
              "QUOTE">"click path"</span>, but in most cases she could also
              get that information by comparing other parts of the log file:
              for example the User-Agent if it isn't a very common one, or
              the user's IP address if it doesn't change between different
              requests.</p>

              <p>Always blocking the referrer, or using a custom one, can
              lead to failures on servers that check the referrer before they
              answer any requests, in an attempt to prevent their content
              from being embedded or linked to elsewhere.</p>

              <p>Both <tt class="LITERAL">conditional-block</tt> and
              <tt class="LITERAL">forge</tt> will work with referrer checks,
              as long as content and valid referring page are on the same
              host. Most of the time that's the case.</p>

              <p><tt class="LITERAL">hide-referer</tt> is an alternate
              spelling of <tt class="LITERAL">hide-referrer</tt> and the two
              can be can be freely substituted with each other. (<span class=
              "QUOTE">"referrer"</span> is the correct English spelling,
              however the HTTP specification has a bug - it requires it to be
              spelled as <span class="QUOTE">"referer"</span>.)</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+hide-referrer{forge}
</pre>
                  </td>
                </tr>
              </table>or

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+hide-referrer{http://www.yahoo.com/}
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="HIDE-USER-AGENT" id=
        "HIDE-USER-AGENT">8.5.25. hide-user-agent</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Try to conceal your type of browser and client operating
              system</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Replaces the value of the <span class=
              "QUOTE">"User-Agent:"</span> HTTP header in client requests
              with the specified value.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>Any user-defined string.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <div class="WARNING">
                <table class="WARNING" border="1" width="90%">
                  <tr>
                    <td class="c6" align="center">Warning</td>
                  </tr>

                  <tr>
                    <td align="left">
                      <p>This can lead to problems on web sites that depend
                      on looking at this header in order to customize their
                      content for different browsers (which, by the way, is
                      <span class="emphasis EMPHASIS c2">NOT</span> the right
                      thing to do: good web sites work
                      browser-independently).</p>
                    </td>
                  </tr>
                </table>
              </div>

              <p>Using this action in multi-user setups or wherever different
              types of browsers will access the same <span class=
              "APPLICATION">Privoxy</span> is <span class=
              "emphasis EMPHASIS c2">not recommended</span>. In single-user,
              single-browser setups, you might use it to delete your OS
              version information from the headers, because it is an
              invitation to exploit known bugs for your OS. It is also
              occasionally useful to forge this in order to access sites that
              won't let you in otherwise (though there may be a good reason
              in some cases).</p>

              <p>More information on known user-agent strings can be found at
              <a href="http://www.user-agents.org/" target=
              "_top">http://www.user-agents.org/</a> and <a href=
              "http://en.wikipedia.org/wiki/User_agent" target=
              "_top">http://en.wikipedia.org/wiki/User_agent</a>.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+hide-user-agent{Netscape 6.1 (X11; I; Linux 2.4.18 i686)}
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="LIMIT-CONNECT" id="LIMIT-CONNECT">8.5.26.
        limit-connect</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Prevent abuse of <span class="APPLICATION">Privoxy</span> as
              a TCP proxy relay or disable SSL for untrusted sites</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Specifies to which ports HTTP CONNECT requests are
              allowable.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>A comma-separated list of ports or port ranges (the latter
              using dashes, with the minimum defaulting to 0 and the maximum
              to 65K).</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>By default, i.e. if no <tt class=
              "LITERAL">limit-connect</tt> action applies, <span class=
              "APPLICATION">Privoxy</span> allows HTTP CONNECT requests to
              all ports. Use <tt class="LITERAL">limit-connect</tt> if
              fine-grained control is desired for some or all
              destinations.</p>

              <p>The CONNECT methods exists in HTTP to allow access to secure
              websites (<span class="QUOTE">"https://"</span> URLs) through
              proxies. It works very simply: the proxy connects to the server
              on the specified port, and then short-circuits its connections
              to the client and to the remote server. This means
              CONNECT-enabled proxies can be used as TCP relays very
              easily.</p>

              <p><span class="APPLICATION">Privoxy</span> relays HTTPS
              traffic without seeing the decoded content. Websites can
              leverage this limitation to circumvent <span class=
              "APPLICATION">Privoxy</span>'s filters. By specifying an
              invalid port range you can disable HTTPS entirely.</p>
            </dd>

            <dt>Example usages:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+limit-connect{443}                   # Port 443 is OK.
+limit-connect{80,443}                # Ports 80 and 443 are OK.
+limit-connect{-3, 7, 20-100, 500-}   # Ports less than 3, 7, 20 to 100 and above 500 are OK.
+limit-connect{-}                     # All ports are OK
+limit-connect{,}                     # No HTTPS/SSL traffic is allowed
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="PREVENT-COMPRESSION" id=
        "PREVENT-COMPRESSION">8.5.27. prevent-compression</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Ensure that servers send the content uncompressed, so it can
              be passed through <tt class="LITERAL"><a href=
              "actions-file.html#FILTER">filter</a></tt>s.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Removes the Accept-Encoding header which can be used to ask
              for compressed transfer.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Boolean.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>N/A</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>More and more websites send their content compressed by
              default, which is generally a good idea and saves bandwidth.
              But the <tt class="LITERAL"><a href=
              "actions-file.html#FILTER">filter</a></tt> and <tt class=
              "LITERAL"><a href=
              "actions-file.html#DEANIMATE-GIFS">deanimate-gifs</a></tt>
              actions need access to the uncompressed data.</p>

              <p>When compiled with zlib support (available since
              <span class="APPLICATION">Privoxy</span> 3.0.7), content that
              should be filtered is decompressed on-the-fly and you don't
              have to worry about this action. If you are using an older
              <span class="APPLICATION">Privoxy</span> version, or one that
              hasn't been compiled with zlib support, this action can be used
              to convince the server to send the content uncompressed.</p>

              <p>Most text-based instances compress very well, the size is
              seldom decreased by less than 50%, for markup-heavy instances
              like news feeds saving more than 90% of the original size isn't
              unusual.</p>

              <p>Not using compression will therefore slow down the transfer,
              and you should only enable this action if you really need it.
              As of <span class="APPLICATION">Privoxy</span> 3.0.7 it's
              disabled in all predefined action settings.</p>

              <p>Note that some (rare) ill-configured sites don't handle
              requests for uncompressed documents correctly. Broken PHP
              applications tend to send an empty document body, some IIS
              versions only send the beginning of the content. If you enable
              <tt class="LITERAL">prevent-compression</tt> per default, you
              might want to add exceptions for those sites. See the example
              for how to do that.</p>
            </dd>

            <dt>Example usage (sections):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Selectively turn off compression, and enable a filter
#
{ +filter{tiny-textforms} +prevent-compression }
# Match only these sites
 .google.
 sourceforge.net
 sf.net

# Or instead, we could set a universal default:
#
{ +prevent-compression }
 / # Match all sites

# Then maybe make exceptions for broken sites:
#
{ -prevent-compression }
.compusa.com/
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="OVERWRITE-LAST-MODIFIED" id=
        "OVERWRITE-LAST-MODIFIED">8.5.28. overwrite-last-modified</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Prevent yet another way to track the user's steps between
              sessions.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes the <span class="QUOTE">"Last-Modified:"</span> HTTP
              server header or modifies its value.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>One of the keywords: <span class="QUOTE">"block"</span>,
              <span class="QUOTE">"reset-to-request-time"</span> and
              <span class="QUOTE">"randomize"</span></p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>Removing the <span class="QUOTE">"Last-Modified:"</span>
              header is useful for filter testing, where you want to force a
              real reload instead of getting status code <span class=
              "QUOTE">"304"</span>, which would cause the browser to reuse
              the old version of the page.</p>

              <p>The <span class="QUOTE">"randomize"</span> option overwrites
              the value of the <span class="QUOTE">"Last-Modified:"</span>
              header with a randomly chosen time between the original value
              and the current time. In theory the server could send each
              document with a different <span class=
              "QUOTE">"Last-Modified:"</span> header to track visits without
              using cookies. <span class="QUOTE">"Randomize"</span> makes it
              impossible and the browser can still revalidate cached
              documents.</p>

              <p><span class="QUOTE">"reset-to-request-time"</span>
              overwrites the value of the <span class=
              "QUOTE">"Last-Modified:"</span> header with the current time.
              You could use this option together with <tt class=
              "LITERAL"><a href=
              "actions-file.html#HIDE-IF-MODIFIED-SINCE">hide-if-modified-since</a></tt>
              to further customize your random range.</p>

              <p>The preferred parameter here is <span class=
              "QUOTE">"randomize"</span>. It is safe to use, as long as the
              time settings are more or less correct. If the server sets the
              <span class="QUOTE">"Last-Modified:"</span> header to the time
              of the request, the random range becomes zero and the value
              stays the same. Therefore you should later randomize it a
              second time with <tt class="LITERAL"><a href=
              "actions-file.html#HIDE-IF-MODIFIED-SINCE">hided-if-modified-since</a></tt>,
              just to be sure.</p>

              <p>It is also recommended to use this action together with
              <tt class="LITERAL"><a href=
              "actions-file.html#CRUNCH-IF-NONE-MATCH">crunch-if-none-match</a></tt>.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Let the browser revalidate without being tracked across sessions
{ +hide-if-modified-since{-60} \
 +overwrite-last-modified{randomize} \
 +crunch-if-none-match}
/
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="REDIRECT" id="REDIRECT">8.5.29.
        redirect</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Redirect requests to other sites.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Convinces the browser that the requested document has been
              moved to another location and the browser should get it from
              there.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>An absolute URL or a single pcrs command.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>Requests to which this action applies are answered with a
              HTTP redirect to URLs of your choosing. The new URL is either
              provided as parameter, or derived by applying a single pcrs
              command to the original URL.</p>

              <p>This action will be ignored if you use it together with
              <tt class="LITERAL"><a href=
              "actions-file.html#BLOCK">block</a></tt>. It can be combined
              with <tt class="LITERAL"><a href=
              "actions-file.html#FAST-REDIRECTS">fast-redirects{check-decoded-url}</a></tt>
              to redirect to a decoded version of a rewritten URL.</p>

              <p>Use this action carefully, make sure not to create
              redirection loops and be aware that using your own redirects
              might make it possible to fingerprint your requests.</p>

              <p>In case of problems with your redirects, or simply to watch
              them working, enable <a href="config.html#DEBUG">debug
              128</a>.</p>
            </dd>

            <dt>Example usages:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Replace example.com's style sheet with another one
{ +redirect{http://localhost/css-replacements/example.com.css} }
 example.com/stylesheet\.css

# Create a short, easy to remember nickname for a favorite site
# (relies on the browser accept and forward invalid URLs to <span class=
"APPLICATION">Privoxy</span>)
{ +redirect{http://www.privoxy.org/user-manual/actions-file.html} }
 a

# Always use the expanded view for Undeadly.org articles
# (Note the $ at the end of the URL pattern to make sure
# the request for the rewritten URL isn't redirected as well)
{+redirect{s@$@&amp;mode=expanded@}}
undeadly.org/cgi\?action=article&amp;sid=\d*$

# Redirect Google search requests to MSN
{+redirect{s@^http://[^/]*/search\?q=([^&amp;]*).*@http://search.msn.com/results.aspx?q=$1@}}
.google.com/search

# Redirect MSN search requests to Yahoo
{+redirect{s@^http://[^/]*/results\.aspx\?q=([^&amp;]*).*@http://search.yahoo.com/search?p=$1@}}
search.msn.com//results\.aspx\?q=

# Redirect remote requests for this manual
# to the local version delivered by Privoxy
{+redirect{s@^http://www@http://config@}}
www.privoxy.org/user-manual/
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="SERVER-HEADER-FILTER" id=
        "SERVER-HEADER-FILTER">8.5.30. server-header-filter</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Rewrite or remove single server headers.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>All server headers to which this action applies are filtered
              on-the-fly through the specified regular expression based
              substitutions.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>The name of a server-header filter, as defined in one of the
              <a href="filter-file.html">filter files</a>.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>Server-header filters are applied to each header on its own,
              not to all at once. This makes it easier to diagnose problems,
              but on the downside you can't write filters that only change
              header x if header y's value is z. You can do that by using
              tags though.</p>

              <p>Server-header filters are executed after the other header
              actions have finished and use their output as input.</p>

              <p>Please refer to the <a href="filter-file.html">filter file
              chapter</a> to learn which server-header filters are available
              by default, and how to create your own.</p>
            </dd>

            <dt>Example usage (section):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
{+server-header-filter{html-to-xml}}
example.org/xml-instance-that-is-delivered-as-html

{+server-header-filter{xml-to-html}}
example.org/instance-that-is-delivered-as-xml-but-is-not

</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="SERVER-HEADER-TAGGER" id=
        "SERVER-HEADER-TAGGER">8.5.31. server-header-tagger</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Enable or disable filters based on the Content-Type
              header.</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Server headers to which this action applies are filtered
              on-the-fly through the specified regular expression based
              substitutions, the result is used as tag.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>The name of a server-header tagger, as defined in one of the
              <a href="filter-file.html">filter files</a>.</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>Server-header taggers are applied to each header on its own,
              and as the header isn't modified, each tagger <span class=
              "QUOTE">"sees"</span> the original.</p>

              <p>Server-header taggers are executed before all other header
              actions that modify server headers. Their tags can be used to
              control all of the other server-header actions, the content
              filters and the crunch actions (<a href=
              "actions-file.html#REDIRECT">redirect</a> and <a href=
              "actions-file.html#BLOCK">block</a>).</p>

              <p>Obviously crunching based on tags created by server-header
              taggers doesn't prevent the request from showing up in the
              server's log file.</p>
            </dd>

            <dt>Example usage (section):</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
# Tag every request with the content type declared by the server
{+server-header-tagger{content-type}}
/

</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="SESSION-COOKIES-ONLY" id=
        "SESSION-COOKIES-ONLY">8.5.32. session-cookies-only</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Allow only temporary <span class="QUOTE">"session"</span>
              cookies (for the current browser session <span class=
              "emphasis EMPHASIS c2">only</span>).</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>Deletes the <span class="QUOTE">"expires"</span> field from
              <span class="QUOTE">"Set-Cookie:"</span> server headers. Most
              browsers will not store such cookies permanently and forget
              them in between sessions.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Boolean.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <p>N/A</p>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>This is less strict than <tt class="LITERAL"><a href=
              "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt>
              / <tt class="LITERAL"><a href=
              "actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt>
              and allows you to browse websites that insist or rely on
              setting cookies, without compromising your privacy too
              badly.</p>

              <p>Most browsers will not permanently store cookies that have
              been processed by <tt class="LITERAL">session-cookies-only</tt>
              and will forget about them between sessions. This makes
              profiling cookies useless, but won't break sites which require
              cookies so that you can log in for transactions. This is
              generally turned on for all sites, and is the recommended
              setting.</p>

              <p>It makes <span class="emphasis EMPHASIS c2">no sense at
              all</span> to use <tt class="LITERAL">session-cookies-only</tt>
              together with <tt class="LITERAL"><a href=
              "actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a></tt>
              or <tt class="LITERAL"><a href=
              "actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a></tt>.
              If you do, cookies will be plainly killed.</p>

              <p>Note that it is up to the browser how it handles such
              cookies without an <span class="QUOTE">"expires"</span> field.
              If you use an exotic browser, you might want to try it out to
              be sure.</p>

              <p>This setting also has no effect on cookies that may have
              been stored previously by the browser before starting
              <span class="APPLICATION">Privoxy</span>. These would have to
              be removed manually.</p>

              <p><span class="APPLICATION">Privoxy</span> also uses the
              <a href=
              "actions-file.html#FILTER-CONTENT-COOKIES">content-cookies
              filter</a> to block some types of cookies. Content cookies are
              not effected by <tt class=
              "LITERAL">session-cookies-only</tt>.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+session-cookies-only
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h4 class="SECT3"><a name="SET-IMAGE-BLOCKER" id=
        "SET-IMAGE-BLOCKER">8.5.33. set-image-blocker</a></h4>

        <div class="VARIABLELIST">
          <dl>
            <dt>Typical use:</dt>

            <dd>
              <p>Choose the replacement for blocked images</p>
            </dd>

            <dt>Effect:</dt>

            <dd>
              <p>This action alone doesn't do anything noticeable. If
              <span class="emphasis EMPHASIS c2">both</span> <tt class=
              "LITERAL"><a href="actions-file.html#BLOCK">block</a></tt>
              <span class="emphasis EMPHASIS c2">and</span> <tt class=
              "LITERAL"><a href=
              "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt>
              <span class="emphasis EMPHASIS c2">also</span> apply, i.e. if
              the request is to be blocked as an image, <span class=
              "emphasis EMPHASIS c2">then</span> the parameter of this action
              decides what will be sent as a replacement.</p>
            </dd>

            <dt>Type:</dt>

            <dd>
              <p>Parameterized.</p>
            </dd>

            <dt>Parameter:</dt>

            <dd>
              <ul>
                <li>
                  <p><span class="QUOTE">"pattern"</span> to send a built-in
                  checkerboard pattern image. The image is visually decent,
                  scales very well, and makes it obvious where banners were
                  busted.</p>
                </li>

                <li>
                  <p><span class="QUOTE">"blank"</span> to send a built-in
                  transparent image. This makes banners disappear completely,
                  but makes it hard to detect where <span class=
                  "APPLICATION">Privoxy</span> has blocked images on a given
                  page and complicates troubleshooting if <span class=
                  "APPLICATION">Privoxy</span> has blocked innocent images,
                  like navigation icons.</p>
                </li>

                <li>
                  <p><span class="QUOTE">"<tt class=
                  "REPLACEABLE c5">target-url</tt>"</span> to send a redirect
                  to <tt class="REPLACEABLE c5">target-url</tt>. You can
                  redirect to any image anywhere, even in your local
                  filesystem via <span class="QUOTE">"file:///"</span> URL.
                  (But note that not all browsers support redirecting to a
                  local file system).</p>

                  <p>A good application of redirects is to use special
                  <span class="APPLICATION">Privoxy</span>-built-in URLs,
                  which send the built-in images, as <tt class=
                  "REPLACEABLE c5">target-url</tt>. This has the same visual
                  effect as specifying <span class="QUOTE">"blank"</span> or
                  <span class="QUOTE">"pattern"</span> in the first place,
                  but enables your browser to cache the replacement image,
                  instead of requesting it over and over again.</p>
                </li>
              </ul>
            </dd>

            <dt>Notes:</dt>

            <dd>
              <p>The URLs for the built-in images are <span class=
              "QUOTE">"http://config.privoxy.org/send-banner?type=<tt class=
              "REPLACEABLE c5">type</tt>"</span>, where <tt class=
              "REPLACEABLE c5">type</tt> is either <span class=
              "QUOTE">"blank"</span> or <span class=
              "QUOTE">"pattern"</span>.</p>

              <p>There is a third (advanced) type, called <span class=
              "QUOTE">"auto"</span>. It is <span class=
              "emphasis EMPHASIS c2">NOT</span> to be used in <tt class=
              "LITERAL">set-image-blocker</tt>, but meant for use from
              <a href="filter-file.html">filters</a>. Auto will select the
              type of image that would have applied to the referring page,
              had it been an image.</p>
            </dd>

            <dt>Example usage:</dt>

            <dd>
              <p>Built-in pattern:</p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+set-image-blocker{pattern}
</pre>
                  </td>
                </tr>
              </table>

              <p>Redirect to the BSD daemon:</p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+set-image-blocker{http://www.freebsd.org/gifs/dae_up3.gif}
</pre>
                  </td>
                </tr>
              </table>

              <p>Redirect to the built-in pattern for better caching:</p>

              <table class="c4" border="0" width="90%">
                <tr>
                  <td>
                    <pre class="SCREEN">
+set-image-blocker{http://config.privoxy.org/send-banner?type=pattern}
</pre>
                  </td>
                </tr>
              </table>
            </dd>
          </dl>
        </div>
      </div>

      <div class="SECT3">
        <h3 class="SECT3"><a name="AEN4706" id="AEN4706">8.5.34.
        Summary</a></h3>

        <p>Note that many of these actions have the potential to cause a page
        to misbehave, possibly even not to display at all. There are many
        ways a site designer may choose to design his site, and what HTTP
        header content, and other criteria, he may depend on. There is no way
        to have hard and fast rules for all sites. See the <a href=
        "appendix.html#ACTIONSANAT">Appendix</a> for a brief example on
        troubleshooting actions.</p>
      </div>
    </div>

    <div class="SECT2">
      <h2 class="SECT2"><a name="ALIASES" id="ALIASES">8.6. Aliases</a></h2>

      <p>Custom <span class="QUOTE">"actions"</span>, known to <span class=
      "APPLICATION">Privoxy</span> as <span class="QUOTE">"aliases"</span>,
      can be defined by combining other actions. These can in turn be invoked
      just like the built-in actions. Currently, an alias name can contain
      any character except space, tab, <span class="QUOTE">"="</span>,
      <span class="QUOTE">"{"</span> and <span class="QUOTE">"}"</span>, but
      we <span class="emphasis EMPHASIS c2">strongly recommend</span> that
      you only use <span class="QUOTE">"a"</span> to <span class=
      "QUOTE">"z"</span>, <span class="QUOTE">"0"</span> to <span class=
      "QUOTE">"9"</span>, <span class="QUOTE">"+"</span>, and <span class=
      "QUOTE">"-"</span>. Alias names are not case sensitive, and are not
      required to start with a <span class="QUOTE">"+"</span> or <span class=
      "QUOTE">"-"</span> sign, since they are merely textually expanded.</p>

      <p>Aliases can be used throughout the actions file, but they
      <span class="emphasis EMPHASIS c2">must be defined in a special section
      at the top of the file!</span> And there can only be one such section
      per actions file. Each actions file may have its own alias section, and
      the aliases defined in it are only visible within that file.</p>

      <p>There are two main reasons to use aliases: One is to save typing for
      frequently used combinations of actions, the other one is a gain in
      flexibility: If you decide once how you want to handle shops by
      defining an alias called <span class="QUOTE">"shop"</span>, you can
      later change your policy on shops in <span class=
      "emphasis EMPHASIS c2">one</span> place, and your changes will take
      effect everywhere in the actions file where the <span class=
      "QUOTE">"shop"</span> alias is used. Calling aliases by their purpose
      also makes your actions files more readable.</p>

      <p>Currently, there is one big drawback to using aliases, though:
      <span class="APPLICATION">Privoxy</span>'s built-in web-based action
      file editor honors aliases when reading the actions files, but it
      expands them before writing. So the effects of your aliases are of
      course preserved, but the aliases themselves are lost when you edit
      sections that use aliases with it.</p>

      <p>Now let's define some aliases...</p>

      <table class="c4" border="0" width="100%">
        <tr>
          <td>
            <pre class="SCREEN">
 # Useful custom aliases we can use later.
 #
 # Note the (required!) section header line and that this section
 # must be at the top of the actions file!
 #
 {{alias}}

 # These aliases just save typing later:
 # (Note that some already use other aliases!)
 #
 +crunch-all-cookies = +<a href=
"actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a> +<a href="actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a>
 -crunch-all-cookies = -<a href=
"actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a> -<a href="actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a>
 +block-as-image      = +block{Blocked image.} +handle-as-image
 allow-all-cookies   = -crunch-all-cookies -<a href=
"actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a> -<a href=
"actions-file.html#FILTER-CONTENT-COOKIES">filter{content-cookies}</a>

 # These aliases define combinations of actions
 # that are useful for certain types of sites:
 #
 fragile     = -<a href="actions-file.html#BLOCK">block</a> -<a href=
"actions-file.html#FILTER">filter</a> -crunch-all-cookies -<a href=
"actions-file.html#FAST-REDIRECTS">fast-redirects</a> -<a href=
"actions-file.html#HIDE-REFERER">hide-referrer</a> -<a href=
"actions-file.html#PREVENT-COMPRESSION">prevent-compression</a>

 shop        = -crunch-all-cookies -<a href=
"actions-file.html#FILTER-ALL-POPUPS">filter{all-popups}</a>

 # Short names for other aliases, for really lazy people ;-)
 #
 c0 = +crunch-all-cookies
 c1 = -crunch-all-cookies
</pre>
          </td>
        </tr>
      </table>

      <p>...and put them to use. These sections would appear in the lower
      part of an actions file and define exceptions to the default actions
      (as specified further up for the <span class="QUOTE">"/"</span>
      pattern):</p>

      <table class="c4" border="0" width="100%">
        <tr>
          <td>
            <pre class="SCREEN">
 # These sites are either very complex or very keen on
 # user data and require minimal interference to work:
 #
 {fragile}
 .office.microsoft.com
 .windowsupdate.microsoft.com
 # Gmail is really mail.google.com, not gmail.com
 mail.google.com

 # Shopping sites:
 # Allow cookies (for setting and retrieving your customer data)
 #
 {shop}
 .quietpc.com
 .worldpay.com   # for quietpc.com
 mybank.example.com

 # These shops require pop-ups:
 #
 {-filter{all-popups} -filter{unsolicited-popups}}
  .dabs.com
  .overclockers.co.uk
</pre>
          </td>
        </tr>
      </table>

      <p>Aliases like <span class="QUOTE">"shop"</span> and <span class=
      "QUOTE">"fragile"</span> are typically used for <span class=
      "QUOTE">"problem"</span> sites that require more than one action to be
      disabled in order to function properly.</p>
    </div>

    <div class="SECT2">
      <h2 class="SECT2"><a name="ACT-EXAMPLES" id="ACT-EXAMPLES">8.7. Actions
      Files Tutorial</a></h2>

      <p>The above chapters have shown <a href="actions-file.html">which
      actions files there are and how they are organized</a>, how actions are
      <a href="actions-file.html#ACTIONS">specified</a> and <a href=
      "actions-file.html#ACTIONS-APPLY">applied to URLs</a>, how <a href=
      "actions-file.html#AF-PATTERNS">patterns</a> work, and how to define
      and use <a href="actions-file.html#ALIASES">aliases</a>. Now, let's
      look at an example <tt class="FILENAME">match-all.action</tt>,
      <tt class="FILENAME">default.action</tt> and <tt class=
      "FILENAME">user.action</tt> file and see how all these pieces come
      together:</p>

      <div class="SECT3">
        <h3 class="SECT3"><a name="AEN4770" id="AEN4770">8.7.1.
        match-all.action</a></h3>

        <p>Remember <span class="emphasis EMPHASIS c2">all actions are
        disabled when matching starts</span>, so we have to explicitly enable
        the ones we want.</p>

        <p>While the <tt class="FILENAME">match-all.action</tt> file only
        contains a single section, it is probably the most important one. It
        has only one pattern, <span class="QUOTE">"<tt class=
        "LITERAL">/</tt>"</span>, but this pattern <a href=
        "actions-file.html#AF-PATTERNS">matches all URLs</a>. Therefore, the
        set of actions used in this <span class="QUOTE">"default"</span>
        section <span class="emphasis EMPHASIS c2">will be applied to all
        requests as a start</span>. It can be partly or wholly overridden by
        other actions files like <tt class="FILENAME">default.action</tt> and
        <tt class="FILENAME">user.action</tt>, but it will still be largely
        responsible for your overall browsing experience.</p>

        <p>Again, at the start of matching, all actions are disabled, so
        there is no need to disable any actions here. (Remember: a
        <span class="QUOTE">"+"</span> preceding the action name enables the
        action, a <span class="QUOTE">"-"</span> disables!). Also note how
        this long line has been made more readable by splitting it into
        multiple lines with line continuation.</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
{ \
 +<a href=
"actions-file.html#CHANGE-X-FORWARDED-FOR">change-x-forwarded-for{block}</a> \
 +<a href="actions-file.html#HIDE-FROM-HEADER">hide-from-header{block}</a> \
 +<a href=
"actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker{pattern}</a> \
}
/ # Match all URLs

</pre>
            </td>
          </tr>
        </table>

        <p>The default behavior is now set.</p>
      </div>

      <div class="SECT3">
        <h3 class="SECT3"><a name="AEN4792" id="AEN4792">8.7.2.
        default.action</a></h3>

        <p>If you aren't a developer, there's no need for you to edit the
        <tt class="FILENAME">default.action</tt> file. It is maintained by
        the <span class="APPLICATION">Privoxy</span> developers and if you
        disagree with some of the sections, you should overrule them in your
        <tt class="FILENAME">user.action</tt>.</p>

        <p>Understanding the <tt class="FILENAME">default.action</tt> file
        can help you with your <tt class="FILENAME">user.action</tt>,
        though.</p>

        <p>The first section in this file is a special section for internal
        use that prevents older <span class="APPLICATION">Privoxy</span>
        versions from reading the file:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
##########################################################################
# Settings -- Don't change! For internal Privoxy use ONLY.
##########################################################################
{{settings}}
for-privoxy-version=3.0.11
</pre>
            </td>
          </tr>
        </table>

        <p>After that comes the (optional) alias section. We'll use the
        example section from the above <a href=
        "actions-file.html#ALIASES">chapter on aliases</a>, that also
        explains why and how aliases are used:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
##########################################################################
# Aliases
##########################################################################
{{alias}}

 # These aliases just save typing later:
 # (Note that some already use other aliases!)
 #
 +crunch-all-cookies = +<a href=
"actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a> +<a href="actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a>
 -crunch-all-cookies = -<a href=
"actions-file.html#CRUNCH-INCOMING-COOKIES">crunch-incoming-cookies</a> -<a href="actions-file.html#CRUNCH-OUTGOING-COOKIES">crunch-outgoing-cookies</a>
 +block-as-image      = +block{Blocked image.} +handle-as-image
 mercy-for-cookies   = -crunch-all-cookies -<a href=
"actions-file.html#SESSION-COOKIES-ONLY">session-cookies-only</a> -<a href=
"actions-file.html#FILTER-CONTENT-COOKIES">filter{content-cookies}</a>

 # These aliases define combinations of actions
 # that are useful for certain types of sites:
 #
 fragile     = -<a href="actions-file.html#BLOCK">block</a> -<a href=
"actions-file.html#FILTER">filter</a> -crunch-all-cookies -<a href=
"actions-file.html#FAST-REDIRECTS">fast-redirects</a> -<a href=
"actions-file.html#HIDE-REFERER">hide-referrer</a>
 shop        = -crunch-all-cookies -<a href=
"actions-file.html#FILTER-ALL-POPUPS">filter{all-popups}</a>
</pre>
            </td>
          </tr>
        </table>

        <p>The first of our specialized sections is concerned with
        <span class="QUOTE">"fragile"</span> sites, i.e. sites that require
        minimum interference, because they are either very complex or very
        keen on tracking you (and have mechanisms in place that make them
        unusable for people who avoid being tracked). We will simply use our
        pre-defined <tt class="LITERAL">fragile</tt> alias instead of stating
        the list of actions explicitly:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
##########################################################################
# Exceptions for sites that'll break under the default action set:
##########################################################################

# "Fragile" Use a minimum set of actions for these sites (see alias above):
#
{ fragile }
.office.microsoft.com           # surprise, surprise!
.windowsupdate.microsoft.com
mail.google.com
</pre>
            </td>
          </tr>
        </table>

        <p>Shopping sites are not as fragile, but they typically require
        cookies to log in, and pop-up windows for shopping carts or item
        details. Again, we'll use a pre-defined alias:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
# Shopping sites:
#
{ shop }
.quietpc.com
.worldpay.com   # for quietpc.com
.jungle.com
.scan.co.uk
</pre>
            </td>
          </tr>
        </table>

        <p>The <tt class="LITERAL"><a href=
        "actions-file.html#FAST-REDIRECTS">fast-redirects</a></tt> action,
        which may have been enabled in <tt class=
        "FILENAME">match-all.action</tt>, breaks some sites. So disable it
        for popular sites where we know it misbehaves:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
{ -<a href="actions-file.html#FAST-REDIRECTS">fast-redirects</a> }
login.yahoo.com
edit.*.yahoo.com
.google.com
.altavista.com/.*(like|url|link):http
.altavista.com/trans.*urltext=http
.nytimes.com
</pre>
            </td>
          </tr>
        </table>

        <p>It is important that <span class="APPLICATION">Privoxy</span>
        knows which URLs belong to images, so that <span class=
        "emphasis EMPHASIS c2">if</span> they are to be blocked, a substitute
        image can be sent, rather than an HTML page. Contacting the remote
        site to find out is not an option, since it would destroy the loading
        time advantage of banner blocking, and it would feed the advertisers
        information about you. We can mark any URL as an image with the
        <tt class="LITERAL"><a href=
        "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt> action,
        and marking all URLs that end in a known image file extension is a
        good start:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
##########################################################################
# Images:
##########################################################################

# Define which file types will be treated as images, in case they get
# blocked further down this file:
#
{ +<a href="actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a> }
/.*\.(gif|jpe?g|png|bmp|ico)$
</pre>
            </td>
          </tr>
        </table>

        <p>And then there are known banner sources. They often use scripts to
        generate the banners, so it won't be visible from the URL that the
        request is for an image. Hence we block them <span class=
        "emphasis EMPHASIS c2">and</span> mark them as images in one go, with
        the help of our <tt class="LITERAL">+block-as-image</tt> alias
        defined above. (We could of course just as well use <tt class=
        "LITERAL">+<a href="actions-file.html#BLOCK">block</a> +<a href=
        "actions-file.html#HANDLE-AS-IMAGE">handle-as-image</a></tt> here.)
        Remember that the type of the replacement image is chosen by the
        <tt class="LITERAL"><a href=
        "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a></tt>
        action. Since all URLs have matched the default section with its
        <tt class="LITERAL">+<a href=
        "actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker</a>{pattern}</tt>
        action before, it still applies and needn't be repeated:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
# Known ad generators:
#
{ +block-as-image }
ar.atwola.com
.ad.doubleclick.net
.ad.*.doubleclick.net
.a.yimg.com/(?:(?!/i/).)*$
.a[0-9].yimg.com/(?:(?!/i/).)*$
bs*.gsanet.com
.qkimg.net
</pre>
            </td>
          </tr>
        </table>

        <p>One of the most important jobs of <span class=
        "APPLICATION">Privoxy</span> is to block banners. Many of these can
        be <span class="QUOTE">"blocked"</span> by the <tt class=
        "LITERAL"><a href=
        "actions-file.html#FILTER">filter</a>{banners-by-size}</tt> action,
        which we enabled above, and which deletes the references to banner
        images from the pages while they are loaded, so the browser doesn't
        request them anymore, and hence they don't need to be blocked here.
        But this naturally doesn't catch all banners, and some people choose
        not to use filters, so we need a comprehensive list of patterns for
        banner URLs here, and apply the <tt class="LITERAL"><a href=
        "actions-file.html#BLOCK">block</a></tt> action to them.</p>

        <p>First comes many generic patterns, which do most of the work, by
        matching typical domain and path name components of banners. Then
        comes a list of individual patterns for specific sites, which is
        omitted here to keep the example short:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
##########################################################################
# Block these fine banners:
##########################################################################
{ <a href="actions-file.html#BLOCK">+block{Banner ads.}</a> }

# Generic patterns:
#
ad*.
.*ads.
banner?.
count*.
/.*count(er)?\.(pl|cgi|exe|dll|asp|php[34]?)
/(?:.*/)?(publicite|werbung|rekla(ma|me|am)|annonse|maino(kset|nta|s)?)/

# Site-specific patterns (abbreviated):
#
.hitbox.com
</pre>
            </td>
          </tr>
        </table>

        <p>It's quite remarkable how many advertisers actually call their
        banner servers ads.<tt class="REPLACEABLE c5">company</tt>.com, or
        call the directory in which the banners are stored simply
        <span class="QUOTE">"banners"</span>. So the above generic patterns
        are surprisingly effective.</p>

        <p>But being very generic, they necessarily also catch URLs that we
        don't want to block. The pattern <tt class="LITERAL">.*ads.</tt> e.g.
        catches <span class="QUOTE">"nasty-<span class=
        "emphasis EMPHASIS c2">ads</span>.nasty-corp.com"</span> as intended,
        but also <span class="QUOTE">"downlo<span class=
        "emphasis EMPHASIS c2">ads</span>.sourcefroge.net"</span> or
        <span class="QUOTE">"<span class=
        "emphasis EMPHASIS c2">ads</span>l.some-provider.net."</span> So here
        come some well-known exceptions to the <tt class="LITERAL">+<a href=
        "actions-file.html#BLOCK">block</a></tt> section above.</p>

        <p>Note that these are exceptions to exceptions from the default!
        Consider the URL <span class=
        "QUOTE">"downloads.sourcefroge.net"</span>: Initially, all actions
        are deactivated, so it wouldn't get blocked. Then comes the defaults
        section, which matches the URL, but just deactivates the <tt class=
        "LITERAL"><a href="actions-file.html#BLOCK">block</a></tt> action
        once again. Then it matches <tt class="LITERAL">.*ads.</tt>, an
        exception to the general non-blocking policy, and suddenly <tt class=
        "LITERAL"><a href="actions-file.html#BLOCK">+block</a></tt> applies.
        And now, it'll match <tt class="LITERAL">.*loads.</tt>, where
        <tt class="LITERAL"><a href="actions-file.html#BLOCK">-block</a></tt>
        applies, so (unless it matches <span class=
        "emphasis EMPHASIS c2">again</span> further down) it ends up with no
        <tt class="LITERAL"><a href="actions-file.html#BLOCK">block</a></tt>
        action applying.</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
##########################################################################
# Save some innocent victims of the above generic block patterns:
##########################################################################

# By domain:
#
{ -<a href="actions-file.html#BLOCK">block</a> }
adv[io]*.  # (for advogato.org and advice.*)
adsl.      # (has nothing to do with ads)
adobe.     # (has nothing to do with ads either)
ad[ud]*.   # (adult.* and add.*)
.edu       # (universities don't host banners (yet!))
.*loads.   # (downloads, uploads etc)

# By path:
#
/.*loads/

# Site-specific:
#
www.globalintersec.com/adv # (adv = advanced)
www.ugu.com/sui/ugu/adv
</pre>
            </td>
          </tr>
        </table>

        <p>Filtering source code can have nasty side effects, so make an
        exception for our friends at sourceforge.net, and all paths with
        <span class="QUOTE">"cvs"</span> in them. Note that <tt class=
        "LITERAL">-<a href="actions-file.html#FILTER">filter</a></tt>
        disables <span class="emphasis EMPHASIS c2">all</span> filters in one
        fell swoop!</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
# Don't filter code!
#
{ -<a href="actions-file.html#FILTER">filter</a> }
/(.*/)?cvs
bugzilla.
developer.
wiki.
.sourceforge.net
</pre>
            </td>
          </tr>
        </table>

        <p>The actual <tt class="FILENAME">default.action</tt> is of course
        much more comprehensive, but we hope this example made clear how it
        works.</p>
      </div>

      <div class="SECT3">
        <h3 class="SECT3"><a name="AEN4905" id="AEN4905">8.7.3.
        user.action</a></h3>

        <p>So far we are painting with a broad brush by setting general
        policies, which would be a reasonable starting point for many people.
        Now, you might want to be more specific and have customized rules
        that are more suitable to your personal habits and preferences. These
        would be for narrowly defined situations like your ISP or your bank,
        and should be placed in <tt class="FILENAME">user.action</tt>, which
        is parsed after all other actions files and hence has the last word,
        over-riding any previously defined actions. <tt class=
        "FILENAME">user.action</tt> is also a <span class=
        "emphasis EMPHASIS c2">safe</span> place for your personal settings,
        since <tt class="FILENAME">default.action</tt> is actively maintained
        by the <span class="APPLICATION">Privoxy</span> developers and you'll
        probably want to install updated versions from time to time.</p>

        <p>So let's look at a few examples of things that one might typically
        do in <tt class="FILENAME">user.action</tt>:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
# My user.action file. &lt;fred@example.com&gt;
</pre>
            </td>
          </tr>
        </table>

        <p>As <a href="actions-file.html#ALIASES">aliases</a> are local to
        the actions file that they are defined in, you can't use the ones
        from <tt class="FILENAME">default.action</tt>, unless you repeat them
        here:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
# Aliases are local to the file they are defined in.
# (Re-)define aliases for this file:
#
{{alias}}
#
# These aliases just save typing later, and the alias names should
# be self explanatory.
#
+crunch-all-cookies = +crunch-incoming-cookies +crunch-outgoing-cookies
-crunch-all-cookies = -crunch-incoming-cookies -crunch-outgoing-cookies
 allow-all-cookies  = -crunch-all-cookies -session-cookies-only
 allow-popups       = -filter{all-popups}
+block-as-image     = +block{Blocked as image.} +handle-as-image
-block-as-image     = -block

# These aliases define combinations of actions that are useful for
# certain types of sites:
#
fragile     = -block -crunch-all-cookies -filter -fast-redirects -hide-referrer
shop        = -crunch-all-cookies allow-popups

# Allow ads for selected useful free sites:
#
allow-ads   = -block -filter{banners-by-size} -filter{banners-by-link}

# Alias for specific file types that are text, but might have conflicting
# MIME types. We want the browser to force these to be text documents.
handle-as-text = -<a href="actions-file.html#FILTER">filter</a> +-<a href=
"actions-file.html#CONTENT-TYPE-OVERWRITE">content-type-overwrite{text/plain}</a> +-<a href="actions-file.html#FORCE-TEXT-MODE">force-text-mode</a> -<a href="actions-file.html#HIDE-CONTENT-DISPOSITION">hide-content-disposition</a>
</pre>
            </td>
          </tr>
        </table>

        <p>Say you have accounts on some sites that you visit regularly, and
        you don't want to have to log in manually each time. So you'd like to
        allow persistent cookies for these sites. The <tt class=
        "LITERAL">allow-all-cookies</tt> alias defined above does exactly
        that, i.e. it disables crunching of cookies in any direction, and the
        processing of cookies to make them only temporary.</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
{ allow-all-cookies }
 sourceforge.net
 .yahoo.com
 .msdn.microsoft.com
 .redhat.com
</pre>
            </td>
          </tr>
        </table>

        <p>Your bank is allergic to some filter, but you don't know which, so
        you disable them all:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
{ -<a href="actions-file.html#FILTER">filter</a> }
 .your-home-banking-site.com
</pre>
            </td>
          </tr>
        </table>

        <p>Some file types you may not want to filter for various
        reasons:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
# Technical documentation is likely to contain strings that might
# erroneously get altered by the JavaScript-oriented filters:
#
.tldp.org
/(.*/)?selfhtml/

# And this stupid host sends streaming video with a wrong MIME type,
# so that Privoxy thinks it is getting HTML and starts filtering:
#
stupid-server.example.com/
</pre>
            </td>
          </tr>
        </table>

        <p>Example of a simple <a href="actions-file.html#BLOCK">block</a>
        action. Say you've seen an ad on your favourite page on example.com
        that you want to get rid of. You have right-clicked the image,
        selected <span class="QUOTE">"copy image location"</span> and pasted
        the URL below while removing the leading http://, into a <tt class=
        "LITERAL">{ +block{} }</tt> section. Note that <tt class="LITERAL">{
        +handle-as-image }</tt> need not be specified, since all URLs ending
        in <tt class="LITERAL">.gif</tt> will be tagged as images by the
        general rules as set in default.action anyway:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
{ +<a href="actions-file.html#BLOCK">block</a>{Nasty ads.} }
 www.example.com/nasty-ads/sponsor\.gif
 another.example.net/more/junk/here/
</pre>
            </td>
          </tr>
        </table>

        <p>The URLs of dynamically generated banners, especially from large
        banner farms, often don't use the well-known image file name
        extensions, which makes it impossible for <span class=
        "APPLICATION">Privoxy</span> to guess the file type just by looking
        at the URL. You can use the <tt class="LITERAL">+block-as-image</tt>
        alias defined above for these cases. Note that objects which match
        this rule but then turn out NOT to be an image are typically rendered
        as a <span class="QUOTE">"broken image"</span> icon by the browser.
        Use cautiously.</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
{ +block-as-image }
 .doubleclick.net
 .fastclick.net
 /Realmedia/ads/
 ar.atwola.com/
</pre>
            </td>
          </tr>
        </table>

        <p>Now you noticed that the default configuration breaks Forbes
        Magazine, but you were too lazy to find out which action is the
        culprit, and you were again too lazy to give <a href=
        "contact.html">feedback</a>, so you just used the <tt class=
        "LITERAL">fragile</tt> alias on the site, and -- <span class=
        "emphasis EMPHASIS c2">whoa!</span> -- it worked. The <tt class=
        "LITERAL">fragile</tt> aliases disables those actions that are most
        likely to break a site. Also, good for testing purposes to see if it
        is <span class="APPLICATION">Privoxy</span> that is causing the
        problem or not. We later find other regular sites that misbehave, and
        add those to our personalized list of troublemakers:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
{ fragile }
 .forbes.com
 webmail.example.com
 .mybank.com
</pre>
            </td>
          </tr>
        </table>

        <p>You like the <span class="QUOTE">"fun"</span> text replacements in
        <tt class="FILENAME">default.filter</tt>, but it is disabled in the
        distributed actions file. So you'd like to turn it on in your
        private, update-safe config, once and for all:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
{ +<a href="actions-file.html#FILTER-FUN">filter{fun}</a> }
 / # For ALL sites!
</pre>
            </td>
          </tr>
        </table>

        <p>Note that the above is not really a good idea: There are
        exceptions to the filters in <tt class="FILENAME">default.action</tt>
        for things that really shouldn't be filtered, like code on
        CVS-&gt;Web interfaces. Since <tt class="FILENAME">user.action</tt>
        has the last word, these exceptions won't be valid for the
        <span class="QUOTE">"fun"</span> filtering specified here.</p>

        <p>You might also worry about how your favourite free websites are
        funded, and find that they rely on displaying banner advertisements
        to survive. So you might want to specifically allow banners for those
        sites that you feel provide value to you:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
{ allow-ads }
 .sourceforge.net
 .slashdot.org
 .osdn.net
</pre>
            </td>
          </tr>
        </table>

        <p>Note that <tt class="LITERAL">allow-ads</tt> has been aliased to
        <tt class="LITERAL">-<a href=
        "actions-file.html#BLOCK">block</a></tt>, <tt class=
        "LITERAL">-<a href=
        "actions-file.html#FILTER-BANNERS-BY-SIZE">filter{banners-by-size}</a></tt>,
        and <tt class="LITERAL">-<a href=
        "actions-file.html#FILTER-BANNERS-BY-LINK">filter{banners-by-link}</a></tt>
        above.</p>

        <p>Invoke another alias here to force an over-ride of the MIME type
        <tt class="LITERAL">application/x-sh</tt> which typically would open
        a download type dialog. In my case, I want to look at the shell
        script, and then I can save it should I choose to.</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
{ handle-as-text }
 /.*\.sh$
</pre>
            </td>
          </tr>
        </table>

        <p><tt class="FILENAME">user.action</tt> is generally the best place
        to define exceptions and additions to the default policies of
        <tt class="FILENAME">default.action</tt>. Some actions are safe to
        have their default policies set here though. So let's set a default
        policy to have a <span class="QUOTE">"blank"</span> image as opposed
        to the checkerboard pattern for <span class=
        "emphasis EMPHASIS c2">ALL</span> sites. <span class=
        "QUOTE">"/"</span> of course matches all URL paths and patterns:</p>

        <table class="c4" border="0" width="100%">
          <tr>
            <td>
              <pre class="SCREEN">
{ +<a href=
"actions-file.html#SET-IMAGE-BLOCKER">set-image-blocker{blank}</a> }
/ # ALL sites
</pre>
            </td>
          </tr>
        </table>
      </div>
    </div>
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